What if it's another Muslim that shoots up a Mosque, say for example a hard core Sunni goes into a Sufi gathering and shoots everyone there?

This sort of mentality from leftwingers is incomprehensible to me. I know they don't believe in personal responsibility whatsoever, but despite that, I still don't understand how one can consistently delude themselves that nothing is ever the fault of the perpetrator, but rather it's because of "society" or "the man" or "the system" causing the perpetrator to take the violent actions they do. And what's more, how they fail to see how this mentality only encourages more and more violence since the perpetrator isn't the responsible party for their actions.