1. turkeys are dumb but killing them is probably still wrong, especially the way it's done, and who wants to eat dead animal? think about the live turkey while you're chowing down. Whose mother did you kill for your own pleasure?
2. it probably isn't good for you, but it sure does taste good. this is not different from anything else you could eat, including pie. except pumpkin, which doesn't even taste good.
3. tradition isn't a valid reason to do anything else, so really this isn't it either. Besides, the tradition is most likely wrong.
4. everyone should go to one of those vegetarian thanksgiving parties where they have a live turkey running around, because that's kind of cool.
5. just eat mashed potatoes, people. :-)