I don't think that this tends to be the case. My impression is that if someone doesn't understand the mainstream positions here, they'll usually be offered corrections unless their position appears to be too confused for explanation to be likely to help. Curi didn't start being downvoted until he started demonstrating poor debate conduct, including exercising double standards himself with regards to scholarship and polite behavior.
My impression is that critiques of lesswrong mainstream positions and arguments for contrary positions are received well and achieve high karma scores when they are of very high quality. Similarly posts and comments that take lesswrong mainstream positions will still be voted down if they are of very low quality. But in between there seems to be a gulf: Moderately low quality mainstream comments will stay at 0 to -1 karma while contra-mainstream comments of (apparently) similar quality score solidly negative karma, moderately high quality mainstream comments achieve good positive karma while similar quality contra-mainstream comments stay at 0 to 2.
Do you share my impression? And if this is the case, should we try to do something about it?