The GOP had no alternative after the Dems retreated from their historical position of single-payer and couldn't even compromise on a public option (apparently Lieberman was the 41st vote against that). The ACA was the GOP plan (Nixon proposed it, the Heritage Foundation wrote policy papers on it, Dole ran on it, Gingrich and Grassley supported it, Romney implemented it in Massachusetts...) and once that was the best the Dems could do, the GOP was left with nothing other than "Obamacare bad!"