[chrisseaton]

Sure, as long as it's not based on a protected characteristic or an interaction subject to a regulation. You have no right to interact with a company otherwise.

[wizzwizz4]

I'm not talking about legal rights; I'm talking about what is a sensible social convention. (Because really, you don't have the right to block anyone.)

[chrisseaton]

You don't need a right to do it, because they have no right for it to not be done.

But social convention was my point - the social convention is it's always fine to block and you never need to explain, in my opinion.