Blair cheated and gambled (no planning for what would happen after Iraq was "liberated") with people's lives. Many see him as a war criminal. It doesn't seem to have done him much harm.
Why did he do it? Probably because it made him feel important to be playing at war with the big boys.
Cameron showed great stupidity and irresponsibility, gambling with the future of his own country, just to fend off his critics for a few years, to give himself more time in power. Again - wanting that status.
I also put some blame on Ed Milliband and on the unions who made him Labour leader. If his brother had become leader, I can imagine him still being leader now, and having won over enough labour voters to win the referendum for Remain. Why do those who are not fit to be leader (Ed and Jeremy) insist on doing the job, rather than putting country and party first? Again, putting self first.
And why did the liberal democrats stand for the referendum - they were part of a coalition government when it was agreed to. Could they not have veto-ed it?
And of course the Remain campaign was an unco-ordinated shambles, run by people who didn't take the risk seriously.
Between them all, they have fucked up our country and its reputation in the world (and the Middle East to boot).