Sure, if you change the morality of a question, it changes the morality of the question. And it’s not illegal to be in the Klan. And BLM protesters did break laws. But the point was not that it’s ok specifically to joke about the Klan getting killed, it’s to illustrate that morality is clearly relevant and intertwined with political belief. People are joking about Trump simply because he’s a Republican. No one’s saying Susan Collins is fair game. It’s because he’s done serious harm and will continue to do serious harm.
Moral relativism is not morality. It’s not “enlightened” to think that because some other people have terrible morality that your own morality shouldn’t guide your beliefs and actions.