Doesn’t discrimination need to be allowed so the site can ban people for things without breaking their own rules? // Banning in one way or annother is kind of the definition of discrimination.

No. It's basically two different meanings associated with the same word:

• "to discriminate" as "to sort out", "to make a distinction" - necessary to ban users
• "to discriminate" as "to treat users differently based on social or individual prejudice" - what people shouldn't be doing

The first meaning is mostly used formally. The second one is kind of "default" when people talk about discrimination.

Are you the same people that say that by banning fascists you're also becoming fascist?

breaking their own rules

While banning people? Impossible