Review Detail of Idkyk in Dragon ball V: Born again as a Saiyan!

I mean it said he was a saiyan, literally every full blooded saiyan that has ever been shown in the canon story has committed genocide. Including Goku. Goku’s might have been more justified since the red ribbon army was trying to take over the world, but he still slaughtered them, and was terribly violent as a baby until he hit his head and rattled his brain, otherwise he’d likely be just like every other saiyan.

and he's reincarnated. your argument is invalid.

Yes, he’s reincarnated as a saiyan. He might have memories of a more preaceful and sheltered life, but he is now a full blooded saiyan warrior, with the same battle instincts and desire for combat ingrained in his DNA. I’m sure he wouldn’t have slaughtered them so easily if they were kind to him and treated him well, but every single member of their species that he met treated him like garbage and tried to kill or otherwise mess with him until he was stronger than them. Of course he’s going to fight back and kill his aggressors. The only exception is the princess, who he killed while out of control in his oozaru form.