Brigadier General Paul W. Tibbets, USAF (Retired), was a man who lived with no regrets at all about his mission. He died today with no regrets either, at 92 years of age.
He stuck around long enough to see what happened on 9/11. And what was his reaction? Yep, you guessed it:

Let’s put it this way. I don’t know any more about these terrorists than you do, I know nothing. When they bombed the Trade Centre I couldn’t believe what was going on. We’ve fought many enemies at different times. But we knew who they were and where they were. These people, we don’t know who they are or where they are. That’s the point that bothers me. Because they’re gonna strike again, I’ll put money on it. And it’s going to be damned dramatic. But they’re gonna do it in their own sweet time. We’ve got to get into a position where we can kill the bastards. None of this business of taking them to court, the hell with that. I wouldn’t waste five seconds on them.

Like I said...no regrets at all. May General Tibbets Rest In Peace.