Most people don't realize that the legislators that write the laws governing healthcare aren't actually affected by any of those laws. State and federal law-makers have their own guaranteed lifetime health insurance plans which are paid for with taxpayer money.
Paul has a pretty effective analogy for this situation. Imagine that there were two sets of roads: One that could only be used by high level politicians, and another for the rest of us. How could the politicians fix problems with our road systems if they only ever drove on theirs.
Luckily, Senators drive on the same roads that we do. If there's a problem with traffic, construction, or potholes, they can talk to the right people and get the problems fixed. Because Senators don't use the same healthcare system that we do, how can we trust them to fix that system?
Well, there's some discussion about forcing legislators to play by the same rules as everyone else:
Obviously this assumes that there is a public option, but it certainly makes sense for Congress to eat their own dogfood. If they come up with a plan good enough for the average American, it should be good enough for the average Congressman as well.