I have seen a ton of false downvotes on mirrors of regressive leftist videos despite the fact the provider of the mirror does not condone the content shown within. Breitbart is a well known victim of this issue.
Do you guys have any advice on how to stop this annoying phenomenon?
No, stop trying to fix the world in useless crusades, rather than effecting changes at the margin that you will actually be able to accomplish.
Besides, downvotes are pluses to the algorithm as much as upvotes.