Ahh okay, yeah, legal issues are important to consider if you are running a public server. (Not so much if it's a private server.)
This is going to be true for any public online service, whether it's federated or not.
It's also going to vary depending on where you are, where the site is hosted etc etc.
I'm not a lawyer, so my article tries to make clear that I can't advise on these particular things.