If the above were true, if this forum didn't also reward group-contrarian ideas as long as they were well presented, how could LW purport to be about rationality?

Is that intended to be an argument? Notice that it is not.

I think the top-voted post you're referring to (link does not work) is by the GiveWell evaluator. Besides writing a good post, he was an outsider with high status paying attention to LW, and Eliezer and everyone supporting SIAI desperately wanted to impress him and make him feel like he was being taken seriously. Not an admittable datapoint.