They could easily be used to intimidate other countries into submission of America's will. However, he immediately saw the potential for misuse of what could basically be an army of super weapons. One would assume that Steve Rogers would be the first one to sign up for anything that had the backing of the United States government.
Millar's stroke of genius was using Captain America, of all people, to lead the rebellion. He believes that by working with S.H.I.E.L.D, he is extending an olive branch that may save them all. He also realizes that it is only a matter of time before the public calls for an outright ban on the use of superhuman powers, and possibly superhumans themselves. His belief is, with every super-human registered, trained by, and working for the government, nothing like that would have to happen again.
Overwhelmed with guilt, he agrees to help push for the Registration Act, and becomes front man for the cause. In the wake of hundreds of children's deaths, Tony is confronted by a grieving mother at her child's funeral. One of them tried to capture Nitro, and the explosion he caused during the fight took out an entire elementary school. Because they were not paying attention to their surroundings, they were unaware of the danger they were placing everyone in. To say it didn't work out for them is an understatement. Not much more than kids, they decided to take on a few villains to boost their reality t.v. It starts with public outcry against all superheroes due to a tragic accident caused by a group of b-list 'heroes'. I can't imagine a comic book fan being for Registration Act! After all, at the heart of all of us, is a geek who is paranoid of anything Big Brother-like. That's not to say that I wasn't rooting for Cap the rebels the entire time. At first, I was sure I would hate Tony, but when I looked at things from his point of view, it was almost impossible not to understand why he thought he was right. I think Millar did an excellent job of showing both sides of this 'Civil War'.