That's a good question! Hate speech as such is also a legal issue[0]. So if you host a platform, you need to comply with the different laws. I think that takes precedence over the different people's definitions. Other than that, I think hosts are entitled to vet their guests for non-protected characteristics, and for one, a group of your users speaking out against another group of your users might not be something you'd like to host. But that's entirely up to the platform's providers, some mind it more than others.

[0] https://en.wikipedia.org/wiki/Hate_speech_laws_by_country