You misunderstand me, RCade,
Yes, there were external people who should have prevented the tragedy and who should have caught the signs.
I agree with you whole-heartedly on this.
What I think plays into his fantasy is where people say "X" pushed him to violence, be it girls, or a bad haircut or lack of sex or, as pegasus pointed out in his rather myopic post, a lack of "the strap".
While others may be blamed for not PREVENTING the tragedy by stopping him, NO ONE but he can be blamed for the actual act.