They're saying identity is important because only relating to an identity creates a community. But that's wrong of course, as many anonymous communities prove. I don't recognize 99% of the posters here either; it is indeed the content that makes the community.

I believe the real explanation of why identity is important to them is a bit of social psychology. The theory is that identifying with people makes them less mean to each other. So they probably want consistent identities so people will be more civil, which is one of their stated goals.