Objectively, you have to convince yourself that the 3,000 some odd dead, like Mike, and 25,000 or so wounded, like Randy, and the 100's of thousands of family members and friends, like Kim and the McMullens, impacted by these deaths and injuries are to be honored, the dead, and comforted, everybody else, by the idea that their sacrifice will keep terrorists off our streets and out of our planes thereby sparing so very many more fellow citizens a horrible fate.
Then, objectively, you have to convince yourself that their sacrifice was the only and best option we had in order to deal with Usama and Saddam and global terror.
Then, objectively, you have to convince yourself that by accepting these losses and continuing a course of action that guarantees more makes you tough and resolved and wise.
Lastly, objectively, you have to convince yourself that whatever it is we may or may not achieve in Iraq by staying it is worth the life and/or limb of another soldier, the life and/or limb of your neighbors kid, your own son or daughter.
There is no snappy last sentence to summarize this post and drive home a point.