Of course, any comment about downvotes is also, understandably, frowned upon and discouraged so there doesn't seem to be much recourse.
We could avoid political or ideological topics altogether but that's very hard considering any conversation can lead to them.
To get back on track, I see it as an extremely hard problem to solve since downvoting due to disagreement is a very big temptation and, once you start, you might not even notice you're doing it anymore.