It's a social manoeuvre, the idea is basically like standing up and clapping to show support. For example, maybe someone wants to support/oppose a position but

It's a social manoeuvre, the idea is basically like standing up and clapping to show support. For example, maybe someone wants to support/oppose a position but is genuinely not the sort of person who believes in making an argument. From that perspective a little public "I disagree and question your character" post is an obvious tactic. The idea isn't to make a point so there isn't normally much reason to respond.