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.

The idea is to make people think about what they say, and maybe not declare themselves the winner in advance. Kinda like you do by declaring what my intentions were.