Here's a thing... If a person is known to be a shameless liar, no matter how similar their political views are to my own, there is no reason to believe they would stick to them when it's no longer convenient.

By the same token, if a person is a ruthless asshole, I'd rather not give them free rein to carry out something I am sympathetic to, because the next I may be the subject of their ruthlessness.

It's sad really, we desperately need the best people to lead us, but politics is so antithetical to ethics that truly wonderful people prefer to do other things.