[dam-buty]

I really don't think the Facebook login is a barrier. Most people have it, and your audience is probably not privacy-anxious hackers but rather happy-go-lucky social media users. I wouldn't bother too much about it.

Adding other social logins, though, would be a good idea. And Github is now an id provider, so why not integrate that? Surely the startup community would feel less blocked by this :)