Buffy
Hey, if that cage could hold Angelus, if need be it can hold you too. Though I really think you're over-reacting. You haven't tried to kill any of us yet, and it's obvious that you aren't some Big Bad or whatever. You're a vampire. Big deal. I'm part demon and a Seer. Dawn comes from mystical origins and wasn't even born in the technical sense of the term. Mantis can make the world explode with his mind.
Besides which, if you leave, you're not protecting anyone. You're just taking one of our biggest fighters and best chances for winning this war out of the equation.