While there are several factors motivating people into supporting this bill, don't underestimate partisan politics. I used to think that applied more to the Republicans, but I've learned over the last year that's not the case.

A LOT of people are partly or largely influenced by the fact that Republicans are (or appearing to in some cases, more on that later) and nut-job right wingers are fighting against healthcare reform. You know, smearing it with buillshit about death panels, abortion, socialism, communism, government takeover, etc.

That makes liberals much more inclined to support the reform (regardless of the actual merits of the bill), and the same goes with many moderate Dems who are already inclined to believe in compromise, etc. Granted, some moderates get scared by the right wing rhetoric, but you get my point.