In the modern Republican Party, tax policy isn't really about tax policy anymore. It's mostly just meant to be evocative, a demonstration that you're really, truly part of the family. So the crazier it is, the better. Nobody—least of all Republican voters—seriously expects any of these proposals to become law.
What's really mind-blowing, though, is the precise nature of the tax policies that rich Republicans have so thoroughly succeeded in adding to the canon. Middle-class conservatives have become completely convinced that "good" tax policies include a flat tax, lower capital gains rates, and repeal of the estate tax, all of which are designed to benefit the rich almost exclusively. It would be as if Democrats had somehow convinced Wall Street that the key to prosperity was higher taxes on yachts, private jets, and Hamptons getaways.