What is so "unhealthy" in pizza?

Cheese is meant to be good for you.
Tomato is meant to be good for you.
Bazil (if going for more italian style) is meant to be good for you.
Some dough. (I don't see how that is bad).
Various meats. (Meat is good for you)

Problem? Only problem I can forsee is if you just stuff your face to excess.