Based on my own experiences being a lone dissenter, the main thing that has allowed me to stand up and maintain my position consistently in the face of uniform opposition and derision, was not expecting much of everyone else in the first place.

For example, in an introductory logic course, when the professor made a mistake, which everyone else in the class agreed with, and I was the sole person to disagree, and attempt to explain it in the face of the entire class brushing me off and laughing about how I thought I knew better when the answer was so obvious to everyone else, it didn't seem weird to me at all that every other person would make the same mistake and I would be the only one to notice it. It wasn't confusing to me, and my success in showing the professor in a couple minutes after class that she had been mistaken after all confirmed for me that my expectations were on track.

Conforming to the beliefs of the crowd is perfectly sensible behavior, in domains where you have no reason to expect yourself to be more accurate than anyone else. Learning to disregard conforming instincts completely is a bad idea, because a lot of the time, it really will be everyone else who's right, and you who's making a stupid mistake which will make you feel like an idiot when you finally realize it. Refusing to conform is both achievable and proper when you have a palpable expectation that other people are going to be stupid.

Unfortunately, it's rather easy for one's expectations of other people's intelligence and rationality to become poorly calibrated.