There are certainly parts of the ACA worth defending. The ACA is clearly better to what the right wing offers, but it is absurd at this point in time to pretend that we should be focusing on working within that paradigm. While the ACA is better than a right wing alternative, you can make a strong case that the ACA is just as inferior to single payer than the right wing alternative is to the ACA as it is. If the 20 states succeed in destroying pre-existing conditions, what exactly is left? The best parts of the ACA were the pre-existing condition protections and the expansion in the public parts of the healthcare system. Both are being undermined. At this point, it should be just as unacceptable to run for office and not support single payer as it is to run for office and not support something like the right to access to public education.
As I have said before though, it says a lot about this political system and the other major party, the Democrats, that the Republicans have the power to do any of this. Their ideas are deeply unpopular, across the board, and only a quarter of the country now identifies with that party. The fact that the Democrats are in the positions says a lot about those that have been in control of that party.