The only "real" reason to be vegan is because of animal rights. I'm gonna try to explain it.
If you're doing it for your health - then there's no point in not wearing wool. If you're doing it for the environment - then you can argue that real fur is better than fake. If you're doing it for the sake of others (like making sure people in poorer countries will have enough food etc) - then why should you be against animal testing?
The difference between being vegan and being vegetarian is simply the lifestyle. Vegans & vegetarians eat the same foods, the only difference is that vegans also says no to all other forms of animal (ab)use.