The food waste argument is, in most cases, ridiculous. You don't select the *exact* size of the pizza, it comes as it comes. Unless you literally count the calories that you get from eating the crust, and then eat other food (that you don't get in a pre-determined size) less the equal amount in calories, it doesn't apply. If you're one of the extremely rare people who literally do that, that's awesome! But let's face it, practically nobody does it.
As for the privilege, everyone living in the western countries is privileged as fuck compared to so many people in the world. Not eating pizza crust, because you don't like it, or because you got full already, will hardly sign your privilege. Jesus.
n00bs7ay3r, I can bet there are tons of people who are way less privileged than you, but choose not to eat the crust, because when they can afford to order pizza, they just want to get the taste and they get full without eating the crust. It might even be that the pizza is a fucking luxury to them, and when they can afford that luxury, they just want to have the good part and couldn't give a fuck about the part they find boring as fuck. In a way, ironically it's sort of privileged to be able to have the time and energy to worry about pizza crusts.
Food waste is a huge problem, but you should apply it primarily when people can select the exact amount of food people can have before getting full.