Sure, he would have been mercilessly attacked by the Tea-Baggers and all the Republicans who are afraid of the Tea-Baggers (which is all of them), but Romney isn't in Congress and isn't running for anything in 2010. The 2012 primaries are still a long ways off and anything can happen between now and then. Hell, just two short months ago, the popular thinking in this country was that Health Care Reform was dead and Obama's presidency was crippled as a result. Who knows what the political landscape will be like a year from now.
Instead, Romney currently finds himself in an impossible position -- he now has to distance himself from legislation that he himself came up with (i.e., RomneyCare in Massachusetts), and you know that his opponents for the 2012 GOP presidential nomination are going to repeatedly point out that ObamaCare is really just RomneyCare. In fact, such attacks have already begun. My point is that Romney was going to be attacked for his Massachusetts plan anyway, so why should he distance himself from it by opposing ObamaCare and in the process look like the Mother of All Flip-Floppers? By expressing support for ObamaCare, Romney could have defended himself from a position of strength and maybe even counter-attacked.
Every other GOP candidate for 2012 is going to be attacking Health Care Reform. Romney could have separated himself from the pack on this issue, and I think it was a big mistake for him not to do that. The GOP plan was to defeat the reform, and by doing so, break Obama's presidency. That strategy failed; but given that every Republican supported the strategy, it was a failure for every Republican. It didn't have to be that way.
By the way, will this be the new GOP anti-reform talking point?
UPDATE: John Cornyn's strategy on how to deal with ObamaCare? Praise it by faintly damning it:
NRSC Chairman John Cornyn plans to send a memo to Republican candidates Tuesday urging them to be proactive in shaping the campaign debate on health care and not let Democrats "distort our record and our ideas." "On the trail, it's critical that we remind people of the fact that it was Republicans who fought to force insurance companies to compete with one another over state lines for Americans' business. It was Republicans who fought to reform the junk lawsuits that raise medical costs and lower quality by forcing doctors to practice 'defensive medicine,'" Cornyn writes, emphasizing the GOP's record beyond its opposition to the Obama-backed health care bill. "It was Republicans who fought for policies that protected Americans with preexisting conditions and it was Republicans who proposed health care reforms that didn't cut Medicare by $500 billion and raise Americans' taxes by $400 million. It's Republicans who continue to believe that we should focus on reforms which actually lower health care costs for Americans, first and foremost." If the GOP thinks health care is going to work to their advantage this year, that doesn't mean they expect that to happen passively.