A pizza needs a crust: a solid and uniform base to support all of the other toppings. It can be as thin as a cracker or as thick as a baguette, but it has to be there. Otherwise all of the things that make pizza worth eating--the tangy sauce, the cheese, the toppings--will never make it to the table. A crust-only pizza is just a boring slice of bread...but a pizza without any crust at all is just a messy, weird soup.
Nobody is suggesting that pizzas don't need a crust. But there is a weird assertion that unless you have a sufficiently dense pizza crust, the cook is going to take advantage of you. I can't wrap my head around that.
(Assuming we're still talking about rules.)