Were I a superhero, I'd have to side with Captain America on this. In real life, I already hate it when I find that I have no choice but to do what someone's cornered me into doing - feeling controlled and maneuvered. I wouldd hate the thought of the government's knowing my secret identity, and thus, knowing who my family and friends are. That'd give the government the leverage to force me to do its bidding - even if I thought its chosen course of action was wrong - by holding my loved ones' well-being over my head. In the face of my possibly becoming government property, I'd be Team Cap in a heartbeat.