US conservatives propose to repeal the Patient Protection and Affordable Care Act, and then replace it with an alternative health reform bill. This would be, perhaps, Rep. Ryan's plan to give each citizen a voucher (a "defined contribution") to purchase health insurance on the private market.
Experts such as Gail Wilensky support defined contribution schemes (others, of course, do not). More importantly, the Ryan plan is clearly superior to repealing the PPACA and leaving tens of millions of Americans without insurance. But that is what would happen if the PPACA was repealed and -- as almost always happens to health insurance bills -- the replacement bill was defeated. In fact, if you have the political capital to pass the Ryan plan, you can certainly pass the Ryan plan with a preamble that eliminated all or part of the PPACA.
So I am perplexed as to why anyone would argue on health policy grounds for 'Repeal, then Replace' instead of just 'Replace.'