Believe it or not, House Speaker Nancy Pelosi, in the course of promoting passage of the Senate version of ObamaCare, said that they need to pass the bill in order for people to really know what's in the bill.
“You’ve heard about the controversies within the bill, the process about the bill, one or the other. But I don’t know if you have heard that it is legislation for the future, not just about health care for America, but about a healthier America, where preventive care is not something that you have to pay a deductible for or out of pocket. Prevention, prevention, prevention—it’s about diet, not diabetes. It’s going to be very, very exciting.
“But we have to pass the bill so that you can find out what is in it, away from the fog of the controversy."
We're not exactly sure why the bill would need to be "passed" in order for people to "find out what is in it". Maybe because, once it's law, people can read it...since the US Code of Laws is actually a public document?