Understanding goes only so far.

I'm really with the Salted Slug on this.

Two brothers who brutally attacked two young boys witnessed serious domestic violence against their mother and had a "toxic home life", a court has heard.

Okay, my understanding is working just fine. On the face of it that's fucking appalling and no kid should be brought up in that kind of environment, but the sad fact of life is that they're not the only ones. Having another five brothers they weren't even the only ones in their family. However, they are the only ones who are on trial for being weird little sadists.

The judge, Mr Justice Keith, has heard how the brothers threatened to kill their victims, then aged nine and 11, stamped on them and attacked them with broken glass, bricks and sticks.
One victim was forced to strip naked and perform a sex act and a metal ring was used to strangle one boy.
The brothers have admitted causing grievous bodily harm with intent.
They have also each pleaded guilty to robbing one of the boys of a mobile phone and the other of cash and have admitted two counts of intentionally causing a child to engage in sexual activity.

Obviously the barrister has a job to do and that is to present the best possible case on behalf of his client. That's what professional legal advocates are there for. With guilty please already made this guy is just there to seek some leniency and argue that his client should not just be treated as a delinquent and depraved mutation, and that's probably not an easy job if all he has to work with is this sort of thing:

The barrister said his client's upbringing could be summarised by a reference in one report to his "toxic home life".
Mr Kelson said his client had been shown horror films at his home when he was as young as 10.
He said the films were "extremely violent" and "gruesome movies in the extreme".

I'm trying to remember when I first saw a horror film, and I think I wasn't a lot older. Perhaps twelve. Can my barrister use that too? Oh hang on, I don't have a barrister, do I? Because I haven't committed a crime.

I'm certainly not arguing that's it's all nature and not nurture that makes people what they are, but nor is nuture the big deal that some would like to think. I've lost count of the number of times someone's childhood or upbringing is brought up as a reason or an excuse for their behaviour or, all too often, their crimes. Okay, perhaps not an excuse but a reason. The thing is that the reason or the excuse isn't necessarily that relevant. There was unarguably a reason why Munir Hussain beat the shit out of someone, but while it wasn't quite good enough to excuse him and overturn the verdict it was sufficient for an appeal judge to suspend the rest of his sentence and have him released (not his brother in law though). The reason there is relevant because there's nothing to suggest that Hussain would brain anyone else with a cricket bat unless they too invaded his home, imprisoned his family and threatened their lives. But if we're to believe a shitty childhood is the reason for two boys becoming sadists then we must also believe that left to their own devices they'd carry on indiscriminately choosing victims to torture for shits and giggles, in which case who really gives a fuck. Tigers can't help being what they are either, but if you found a couple roaming around a South Yorkshire town you wouldn't shrug your shoulders about it. You'd have them caught and removed to somewhere they can't threaten people's safety. The twists of DNA that make them several hundred pounds of stripes, claws, and teeth rather than hooves, horns and beef don't even enter into that decision.

By all means choose to believe that a child is a blank sheet and incapable of evil until or unless exposed to it in their formative years, but as a practical matter don't expect me to show much interest if you tell me that because of it someone has become evil. You might even be right but apart from being something for others to beware of it doesn't change anything. Not what was done to the victims, and not what needs to be done to prevent the perpetrators from finding more victims.