Risks of reputation damage cannot be allowed to override contract law. Instead, they should be able to just point to the contract and tell the deplatforming mob that they have to abide by it.

Otherwise, no contract will be worth the paper it is written on if a mob can just scream on Twitter and get a perfectly legal site taken down on very short notice. I'd be very hesitant to sign a contract with any company that doesn't include extremely high termination fees that would be sufficient to find a new host.

The reputation damage came from removing a platform, not from hosting it

My opinion of Amazon went up ever so slightly by removing Parler.

It should have done it a while ago (violent rhetoric didn't just pop up on there last week), but better late than never.

Both, depending on which side of the aisle you're asking.