I'm not sure if Lemmy collapses heavily downvoted posts like Reddit does, but if it does it is also playing a part in creating an echo chamber.

I personally don't have a very strong opinion about up-/downvotes but in general I try to stick to only downvoting comments that are not contributing or down right hostile. I refuse to downvote a comment that is attempting to discuss something in a proper manner, even if I completely disagree.

I get your point about it being harder to agree than disagreeing with this type of mindset though, so it's not perfect.