I think a lot of parents tend to take the attitude that other people are always to blame. No one wants to take accountability or accept that their child may cause trouble etc. For example, my oldest son had a bully in 3rd grade that chased him around the playground with a pair of scissors and threatened to stab him. Granted they were blunt scissors and so wouldn't have hurt him, but the parents of this child threw a fit because surely the other children provoked him etc. He never got in trouble and was left to his shenanigans
Fast forward to 8th grade where this kid everyone was afraid to discipline got suspended for threatening a kid again - this time with an actual weapon (pocket knife) when he could actually hurt them. I wasn't there, but I bet they had an excuse for that too. Throughout the past several years his behavior has spiraled and he always gets away with it, because someone always shifts blame or sweeps it under the rug etc. If they'd have disciplined this boy the first time, both teachers and the parents, rather than make excuses for him, he may not have felt entitled to bully others to get his own way.
I know on the couple of instances where I received a call from school, I did not just assume my sons innocence and I asked for all sides of the story, taking the opportunity to teach my son how to correct his behavior in the future. My son has never done anything as serious as this kid, but still, I stop it and make him own whatever he does and correct it. The fact he knows we enforce rules and expect certain behavior also deters him from doing things without thinking because he doesn't want the consequences of no video games, being grounded whatever...
Too many parents want to make excuses and blame anyone and everyone but their little cherubs. The result is a bunch of future adults who can't work together or "play" nicely with others - because they will always have a cop-out and someone to blame when things don't go their way.