... will be persuading them to switch to a flat tax in the first place. If the 60% that make up the middle class will see their taxes rise under a flat tax (as appears likely, given your formulation that the middle-class currently is subsidized), the question for you is, how do you persuade them to accept that increase?

Seems to me the most reasonable argument is to portray it as a two-step process: first we switch to flat taxes, then we shrink government down to what we're willing to pay for. But you're asking the middle-class to take it on faith that taxes will go down -- and you're also asking them to believe they will like the result.

This isn't an argument against your theoretical points. Just that, as a flat-tax proponent, you've got a chicken-egg problem to solve if you're going to make it a reality.