I almost never vote down a Hub unless it is so bad that I actually flag it for review by Hub Pages staff. Then it is usually machine translated hubs, gibberish hubs and the like. If it looks like someone actually spent some time writing it I will very rarely vote one down.
I see a lot of political Hubs that I consider close to hate speech, or just stupid and ill-informed. I do NOT vote those down. I also write political Hubs and I would hate for people to get into that habit, so I don't want to start it. For that reason I do not participate in HubPages political forums.