It’s generally safe to assume they mean it, unless proven otherwise.

The sentence you're replying to completely agrees with this. I think you misread it.

Even if the hateful remarks are understood to be ‘‘a joke’’, I don’t think that’s any less damning. These are not the type of things to joke about, and most reasonable and/or decent people realize that.

I was thinking in terms of Jonathan Swift's A Modest Proposal or someone adopting a Colbert-style character, like the one from his old show.

Can you give me an example of something like that playing out on a serious real-life topic such as politics/race/genocide etc?

With politics, it usually comes in the form of verbal abuse.