The reason that you are running into situations like this is because you (the meme creator position) don't witness the Centrist also vehemently argue with right-wing policies frequently.

You only see them argue with you and therefore have a skewed view of them and their politics. If you are left wing, and argue for left-wing policies in every case, that means you will also be argued with by somebody who believes political nuance and not just waving a party flag.

The right wing also shits on centrists because they think they are secretly left-wing since they argue with some of their stupider points as well.

These people are not secretly right-wing and just don't have the balls to say it. That is a horrendous take no matter where you fall on the political spectrum the only serves to limit conversation.