Why *isnt* pizza healthy?

I know Pizza isn't good for you, but why is that? It's made of bread and veggies mostly, with cheese on top. Is it just the cheese that's bad? Would light or no cheese make it better?

Edit: I see, it *can* be pretty good for you, but the bread can have sugar and meat can have preservatives. It's mostly the portioning that hurts you, though. If I want to be health-conscious with pizza, I'm going to either home-make them or get a thin crust with mostly veggies. Thank you!