Out of the shallow villains from DBZ, Broly seems the most so. While Cell was programmed to kill Goku and took joy in facing a strong opponent, or Frieza reveled in conquest and victory, Broly lacked even that much complexity. Broly wanted to kill Goku. Unlike the Androids, he was not programmed to do so by someone with a grudge, unlike Vegeta, it wasn't out of some drive to be stronger. We are meant to believe that as a young child, Broly heard Goku's cries, which etched so deeply in his psyche a hatred for him, that even as an adult, the hatred has only gotten more virulent.
At a cursory glance, this seems one of the weakest reasons for a villain to try and kill Goku. Broly has no other plans, no ambitions. Does he just enjoy destruction for its own sake? However, unlike most of the antagonists Dragon Ball holds, we see Broly's past. We see his family, his origin, and looking deeply, we see something far more tragic than at first glance.
Broly was born on Planet Vegeta, homeworld of the Saiyans, one of the most powerful races to people the galaxy. Despite their strength as a people, they are held in thrall by Lord Frieza, a galactic landlord who sends forces to conquer planets and extinguish their lifeforms to sell to the highest bidder. One might think this life empty for a sentient race, but the Saiyans are more or less amenable to the deal. Saiyans are almost Spartan in temperament, they live for combat. Vanquishing a tough foe is one of their greatest joys, and the other elements that make up a life are secondary. Building civilization, parenting children, creating art, all of these don't matter much to a Saiyan. Their love of war holds such a sway over them that the Saiyans destroyed their original home planet Sadala in a giant civil war. They were forced to find and conquer a new planet just to survive.
Here we come to Paragus, low class warrior and father of Broly. Father means something different to Saiyans than it does for humans. For humans, typically a father and mother conceive and raise a child together, providing it love and support until it has grown up enough to make life on its own. For Saiyans, their children are birthed in pods. They are put in a nursery until such time that their power levels are high enough, then they are shuttled off to some distant, weak planet where, using their natural ferocity, they are meant to destroy its inhabitants. Goku, our main character, averted this fate with the help of his adoptive grandfather Gohan and a well-timed bump on the head, mellowing his tendencies and giving him an appreciation for life.
Broly doesn't even get this chance. Shortly after being born, he's first kept awake by the infant Goku's constant crying. Then his extremely large power level is noticed by the rest of the Saiyans. It comes to be that their king, Vegeta (Not that one) orders the execution of Broly, seeing him as a threat to Planet Vegeta's power structure. In a vain effort to halt their orders, Paragus is attacked by King Vegeta, who then goes on to personally stab a baby. Astonishingly, Paragus and Broly survive, only for the entire planet to be destroyed. You see, at this time, Frieza had put into motion his plan to eradicate the Saiyans and sent an immense ball of energy at the planet. Luckily, Broly was able to seal himself and his father in an energy bubble to safety.
What follows is sparsely known. Paragus and Broly are intergalactic refugees, wandering the cosmos without a home. Broly becomes stronger daily, his power growing as fast as his father's fear. He exibits a sadistic ferocity, wreaking havoc whenever he is able. Eventually, Paragus has a device constructed that will contain Broly and pacify him until such time as he is needed.
Thus follows the events of the film, where Broly and our familiar characters from Earth are caught up in Paragus' convoluted scheme to bring our Vegeta, the son of King Vegeta, to a freshly conquered planet which is set to be demolished by an immense comet. Broly is hardly a part of this plan, though Paragus lures Vegeta to the planet with tales of the Legendary Super Saiyan, Broly is never meant to kill Vegeta. The orchestrated events fail when Goku comes to the planet, awakening Broly's anger and breaking him from Paragus' control. Broly goes on a rampage, all his latent power brimming to the surface, all with the intent to kill Goku and anyone else who will stand up to him. He is seemingly destroyed, not only by Goku, but by his own energy overwhelming his body, causing him to rip apart from the inside.
Though this plot seems efficiently self-contained, we find ourselves asking, why did Broly remember Goku's face, to the point where the anger from the memory caused him to break from his father's power limiter? Why did Broly grow up with such a monstrous disposition?
To begin that discussion, we first have to examine power levels in the Dragon Ball universe. Power level, that is to say your Ki, or fighting energy, is a bit of a nebulous concept, despite being very prevalent in Dragon Ball Z. It's supposedly a simple measure of strength, that is how it is presented as far as Freiza and other villains understand it, but with our heroes on Earth, there's a particular quality that muddies the waters. Goku and friends have the ability to alter their power levels, mostly at will. In their base state, none of their readings look very high, but once engaged in combat their levels raise significantly, sometimes channeled into powerful energy attacks. Though training and strengh is a viable factor in their ki, many times characters, especially Goku, raise their ki through their emotional state. Anger in particular seems to have the greatest effect on this, it is after all what allowed Goku to first reach the state of Super Saiyan.
What I'm trying to say is, despite how ridiculous it sounds for a baby to have a power level of 10,000 when a typical human farmer has a power level of 5, it may have a legitimate reason. Power level has less to do with one's physical capabilities than it does with their mental composition. How could a baby have any sort of mental control? The answer, improbable as it may seem, is simple. Broly was born fully sentient. Each moment from his birth was remembered, though perhaps not fully comprehended, by Broly. Though an infant Saiyan may have more strength than a human baby, what made Broly have such a high level of power was that he was fully conscious from birth. Emotions are integral to harnessing one's ki, and though babies may have a rudimentary form of emotions, it's only when one has matured enough to identify and exploit an emotional state that any sophisticated ki control is possible. Though lacking any true intelligence at that tender age, Broly had a far more complete view of his world than any other Saiyan child at his age. If circumstances were different, it's possible Broly could have become a prodigy. He certainly started far ahead of his cohorts, but as we can see, events transpired to lock him into a far different path. Because of his unique psychology, he was able to remember being kept awake by Goku, he was able to notice the planet's destruction and use his latent power to save not only himself, but his father.
His very first memories were of trauma. After his attempted murder and miraculous escape, it's clear what kind of effect they had on Broly. Etched deep into his mind were visions of violence and death. It was the only way he knew to interact with the world. As his sadism grew, his father, the only person he had ever known, began to fear him. Even a Saiyan, one of those who revel in combat and destruction, was taken aback by Broly's behavior. How could he know any better? A normal child would be impressionable, and with Broly's particular psychology those early events held a much more prominent place in his formative moments.
Due to his fear, Paragus was completely unable to deal with Broly. Instead, he resorted to the power limiting device, a headband wirelessly connected to a gauntlet Paragus held. The question is, how did it work? When under the influence of the device, Broly was not only weaker, he was docile. He was quiet, unassuming, and obeyed orders. He was in complete opposition to the Broly we see in flashbacks, and that is for one reason. In order to control his power, the limiter blunted Broly's mind. One might assume that once Broly was no longer a threat, Paragus could try to help him. Instead, Paragus used Broly like a tool. He made Broly conquer planets for him and subjugate civilizations, working towards his ultimate goal to kill Vegeta. This would eventually end disastrously for Paragus.
It was inevitable that Broly would break his father's control. His power, despite the limiter, continued to grow, only requiring one last push to sever the bonds. Cue Goku. Broly is confronted with the very first misstep in his disaster of a life. That primal memory, buried by heinous acts he committed was unearthed, sparking a rage unlike any Broly had ever experienced. Paragus' device was a crude bandage covering an all-encompassing infection and once it had been removed the putrid flesh was revealed for all to see. His power seemed to rip its way out of his body in a far more violent transformation than any other character undertakes.
Once unleashed, Broly's intelligence returned, but along with it he became more sadistic than ever, throwing around his opponents, disobeying his father's commands, even obliterating another planet just to taunt an alien child. He mirrored his own tragic circumstances in this child, because for Broly that is the natural order. He was born into that world and he never had to chance to learn there was anything more. He was past the point of no return, destruction hard-wired into his soul. After murdering his father, Broly is finally defeated. Though Goku seemed to be responsible for punching Broly so hard he exploded, there's more to it than that. Broly's ki had been increasing since severing his father's control, until it reached a point where his body couldn't handle it. In the end, his own power destroyed him.
From the moment Broly was born he had not had a moment of peace. His mother never held him, he never had any bodily contact with another living being until the day a man tried to murder him. Shortly after birth, his entire existence was thrown into chaos, a roaming renegade life without stability. The very ground underneath him was annihilated while he was left for dead in a quarry. And before that, in what could have been the only tranquil time to hold on to, he was kept constantly awake by the endless piercing cries of Kakarot. His father was too weak and afraid to put Broly on a better path, resorting to sedating Broly and using him like a weapon. Broly never learned of a peaceful life, never trained to keep his power in check. Broly was never treated with tenderness or care, never had the chance to become a well-rounded human being.
What we see with Broly is a story of tragic circumstances and failed opportunities. A quirk of fate, an exceptional child, had the potential to become the paragon of his species. Instead, because of conflicts far beyond his reach, an inept caregiver, and one crying child, he became a monster. He became something reprehensible, but must our feelings towards him be so simple? Broly deserved more than he ever received, and I think we can reserve some feelings of sympathy for our erstwhile Legendary Super Saiyan.