I think there was a notion that all these countries would eagerly transform into nice little European-style liberal democracies, and all those nasty human rights issues would be a thing of the past. Look how that turned out.
I suspect the root cause of Gulf War 2 was Dubya wanting to avenge daddy, and Blair wanting to be his obedient servant, although the truth will probably never come out.
If we could have established a 'don't f*** with us and we won't f*** with you' relationship with Saddam and Gadaffi the world would probably now be a safer place. These dictators had woodchippers and meathooks to deal with the kind of people that are now commanding territory across Syria and Iraq.