Flip-flopping, hardly more noble, usually represents a politician's craven recognition that a pander isn't working. Quantum pandering is not about the times changing, but rather the need to appease two irreconcilable points of view at the same time.
Yes, there is plenty to criticize Portman about, but at least he seems to have made peace with himself and his son -- something that is still so elusive to millions of Americans. Perhaps that should count for something.
As a political flip-flopper myself, I will not criticize Bachmann's conversion. I just find her stated reasons flimsy. I don't think we need to bring patriotism into a discussion of our political affiliations.