To be fair, Mitt has made a lot of noises about how Romneycare is distinctly inappropriate at a Federal level, to the point of promising to exempt all 50 states from Obamacare once he became president. Some of Romneycare’s advisors did go on to provide input to Obamacare, but this was without Romney’s own endorsement, AFAIK. If there’s documentation that Romney himself secretly advanced Obamacare planning, that’s a whole different ballgame.
It’s other things than Obamacare that are a more serious issue with Romney. Romney would be a big spending liberal in other Federalized social programs and would be a mush on things like 2nd amendment rights.
Romney’s liberalism is more objectionable than his embrace of RomneyCare. Its one thing to support a disastrous state experiment. Its another thing to have a consistently liberal record. That’s why people don’t trust him. Slick is the word that comes to mind with Mittens - he’s just unprincipled and his only real concern to get elected.