It is if you've already made up your mind that Jordan Peterson, for example, is a piece of shit and therefore nothing anyone says about the matter really matters anymore.

The people downvoting him already made up their minds. They already came to the conclusion they think is correct, and so debate is no longer needed. To them, you're needlessly drawing out an argument that has long since ended in their favor, and why would anyone do that unless they had an ulterior motive?

That's how they think. They're not really wrong; whether they're upvoting misinformation or not really IS irrelevant to the grander question and that grander question is whether JP is a fraud, and to them that answer is unequivocally yes, debate over.

Don't waste your time arguing with them. Their battle lines have already been drawn.