He was going through a lot as a kid. What he did with toys was both a hobby, and a way of releasing his frustrations in a way that isn't a life of crime, nor hurting any actual people. Or so he thought.
Yes, we the audience knew the toys where alive, could feel pain, and he was torturing them, but guess who didn't know that?
The only thing he ever really did that was wrong was he broke a arcade machine and used his sister's doll for a DR Deranged rollplay without her permission. Which, you know, was someone else's toy. But to be fair it was somthing he could easily reverse and make the toy normal again so he probibly didn't see why it was a big deal. But the arcade machine is without excuse.