The forums on the internet should not be solely to affirm your opinions, but also to challenge them and allow growth as an individual.
The problem isn't with politics -- it's with the people misusing the voting system.
I would be surprised if this had much of an impact. I've encountered a lot of people even on HN who truly seem to believe their ideology is somehow 'fact'. Those who are sufficiently self-aware in this regard are probably not abusing the downvote button to begin with.