Lemmy.world instance policy towards obvious troll user?

Someone isn't a troll just because they disagree with you on something or have been brainwashed into not believing in the real world. You're better off engaging these people politely and calmly and bringing them out of their stupidity...or just use the block function. Visit their user page, and hit block.

Downvote and carry on.

Don't feed the trolls.