Not all the heros may be fighting to protect their own identities, but rather fighting to protect the identities of their friends. Or more importantly, fighting agaist a law they see as unfair regardless of if it effects them personally or not. The same as you'd expect some non-mutants to protest a mutant registration act.
It's about fighting for what you bvelieve is right. And what you might consider "right" may be no where near what your neighbor considers right.