This is indeed a good point — based on the ad hoc constitutional arguments made by most Republicans, Paul Ryan is proposing to completely destroy American freedom by replacing Medicare with a mandate to purchase insurance. I expect him to force Americans to eat fried cheese curds next!
Of course, Republicans will just go back to the correct position that there’s nothing unconstitutional about mandates — just as they did when Social Security privatization was being proposed. Ryan’s plan is just an excellent illustration of how unserious the argument always was.
…Simon Lazurus also made this point.