There seems to be a lot of discussion these days about Iraq, even on this site, which I think can be handled in one easy illustration.
If your family was mugged, and the mugger without question is going to shoot and kill them, but you have the opportunity to shoot and kill the mugger first, would you not do it? No time to discuss the consequences with the mugger, cannot discuss with said mugger on how he would "feel" if you shot him, no time for anything. If you do not react, he will kill your family without question, without hesitation. Very simple. Family dies, or the mugger dies. It really is that simple. Which do you chose? I would sincerely hope that each one of us would absolutely save our family at whatever cost. This is not to suggest that any one of us wants to kill, however this is an extreme situation.
The mugger is Saddam and the other terrorists out there. The family is ourselves, our friends, our family, our country, our way of life. If we do not stop him now, we will suffer the consequences. It is either him, or us. It really is that simple.