There's no problem with identifying with arguments and wanting to defend certain positions if you are open to arguments and evidence against your position. It's actually convenient to do so for the purposes of discussion and advocacy.

Most people here are probably "transhumanists", which connects their beliefs to their identity, but that doesn't mean they wouldn't change their mind or alter their beliefs if they see evidence against transhumanism. Describing specific traits that apply to you and your positions shouldn't make you reluctant to change your positions, and also identifying with specific advocacy groups is probably inevitable.

I don't think you're really addressing what Wei Dai's original post is actually discussing. I think that it should be apparent that Wei Dai isn't advocating having more closeminded commenters, but is advocating a more diverse set of viewpoints and advocacies. You're dismissing the overall idea was trying to be reached at based on an interpretation of "contrarian" that doesn't make sense when viewed in the context of the advocacy statement within the original post. Even if you're right about what "contrarian" means, please mentally replace every instance of "contrarian" with "person advocating something unpopular", and that will make this discussion much more productive.

I agree that tying one's identity to opposition specifically is bad, though. That's political paralysis as a consequence of misguided cynicism. If you reject every position then you can advocate nothing. That's not just ineffective, it's a horrible way to live. Affirmation is good.