There are lots of reasons to be against nationalized healthcare. Some for practical reasons, others for legal reasons -- just because you want something doesn't mean it can skip the legal process which is what obamacare tries to do in a lot of places.
One simple reason to be against it is that the current implementation is crazy bad and has no way of dealing with costs and is anti-democratic. It creates outside bodies that don't answer to congress, etc.
Citations needed. The primary argument used against ACA's constitutionality was struck down by the supreme court [1]. And there already exists at least 50 government agencies that reserve the right to pass regulations without congressional approval [2].
One simple reason to be against it is that the current implementation is crazy bad and has no way of dealing with costs and is anti-democratic. It creates outside bodies that don't answer to congress, etc.