You sometimes see pizza included in a list of junk food. But is pizza junk food? My answer is a qualified no. The original Italian pizza is a dough base with tomato, mozzarella cheese and olive oil. Some herbs may be added. Other toppings may be added, of course. What you should not do as a rule is overload the pizza with cheese and other ingredients, especially meat.
Another caveat is frequency. What is often harmful about food is that certain things are eaten too often. You should not be eating pizza (or hamburgers, or hot dogs, or fries) several times a week. Almost anything goes in moderation. And be honest with yourself in defining "moderation".