I was momentarily confused by this "nobody has a right not to be offended" as meaning "Everyone has a duty to be offended", rather than "Nobody has a right to be shielded from exposure to that which offends them", which is what we're actually talking about. Alternatively, "Everyone must reasonably expect to encounter at times that which offends them, and should not expect redress on every such occasion".

But your response to this question is a good one.