We do know now that Saddam Hussein posed no credible threat when we invaded, and containing him cost billions per year less than the current costs.
Just because our men and women volunteer does not mean that poor decisions made by leadership that get them in extremis should be ignored. Military men and women volunteer with the knowledge that they will not be sacrificed needlessly, and that any decision to send them into combat will be carefully made.
To say that "They volunteered, so... (shrug)", makes me question your decision making capability regarding leadership. I would hate it if a CO of mine sent a buddy on a mission with failure written all over it and said "Well, he volunteered to serve and by doing so accepted the risks of his duty", thereby absolving himself of the real responsibility.