Being a monster is a choice:

We really need to bring an end to the myth that monsters are sick/victims themselves, or indeed anything other that entirely normal people who choose to do monstrous things.

The vast majority of abuse victims do not become monsters and many people who become monsters have perfectly average non-abusive child hoods.

The myth that a monster is sick/a victim hurts actual victims in several ways.

The assumption of mental illness/sickness, it stigmatizes people who are mentally ill.

The assumption that abuse leads to the creation of monsters not only fuels stigmatization of actual victims/survivors since it's easy to assume that it is only a matter of time before we snap, it also undermines the self belief of the victims/survivors. Imagine being told that what you went through turns people into monsters, do you have any idea of the kind of fear and terror of the idea that you will automatically become a monster causes?  Btw, it's pretty awful, just so you know. As if we didn't have enough to deal with, we suffer abuse, and then there's victim blaming and this shit. Which also lets our abusers off the hook by blaming their actions on abuse/sickness instead of on the real reason for most abuse.

What really makes a monster? The choice.

When you get down to it the majority of abusers? Are self entitled assholes. They think their violence and abuse is justified because they feel entitled to treat others like that. The majority of the time when people do nasty things to other people, even if it's not outright abuse? They do it because they think they are in the right. Self entitlement is the most toxic of human viewpoints, and it is one that is chosen.

Self entitlement is a function of privilege, so it's little wonder that, violence, murder, rape, and domestic violence is primarily committed by men. It's little wonder that the majority of spree killers are white men.
Anyone can choose to harm others. Anyone can self justify harming others. Those are not functions of being mentally ill or being abused, those are functions of being human with the ability to choose how we act and treat others. We can choose to be self entitled about our privilege, or we can choose not to be. It is that choice that determines if we are a monster.

We need to be talking about the role privilege plays in monsterhood, not playing "monsters aren't normal" because they bloody well are, they simply make a choice to be a monster. Monsters are normal people, they aren't mentally ill, they aren't abused victims most of the time, they aren't abnormal, they're just self entitled and capable of self justifying what they do.