There is one fact that is both central to the debate over repealing the Affordable Care Act yet strangely absent from explicit discussion about it. One of the main ways the ACA makes health insurance affordable is by providing families earning less than 400 percent of the poverty line (i.e.,less than $85,000 for a family of three or less than $47,550 for a single person) with tax credits to defray the cost of purchasing insurance. Giving people money helps make things more affordable.
President Obama and the congressional Democrats who wrote the law didn't find the money for those subsidies hidden in a banana stand — they did what Democrats like to do when paying for things and raised taxes on affluent families.
Republicans do not like this idea. They dislike the idea of raising taxes on wealthy households so much that back in 2011, they pushed the country to the brink of defaulting on the national debt rather than agree to rescind George W. Bush's high-end tax cuts. In December 2012, they tried to insist that they wouldn't let Obama extend the portion of the Bush tax cuts that everyone (including rich people) got unless he also extended the tax cuts that only rich people got.
All of which is to say that despite Democrats' occasional protestations of bafflement as to why the GOP would so uniformly oppose a market-based approach to universal health care that Mitt Romney happily adopted in the mid-aughts in Massachusetts, there's no real mystery here. Subsidizing the health care costs of working-class people is expensive, and while Democrats want rich people to pay the freight for doing it, Republicans do not.
That's an important reason why they opposed the Affordable Care Act, it's an important reason why they want to repeal it, it's an important reason why they can't replace it with something better, and it's also an important reason why they may end up just dropping the whole thing.