Everything isn't to be treated as a debate in good faith. It is very, very rare for a person to be making inflammatory comments in an earnest attempt to start a debate in good faith. I agree, if the platform is a debate-like context, it would be bad form to do that.

But if you walk into a bar or post on Twitter talking about how much you dislike ___, don't be surprised if someone has a reaction. I certainly won't be inclined to start a Socratic dialogue exploring why you dislike ___ in an attempt to persuade you.

You wouldn't spout a racist manifesto on a talk show, don't expect to be able to do it on a medium that everyone can see and think nothing will come of it. You need to be acutely aware of your audience and reach when you speak.

In this context, do not be surprised if people cannot separate their judgment of the comment from the person making it. Especially when the context is "I just read this awful comment on my screen by a person I don't know and already dislike."