I do think that Kim and I were brothers in a prior life, and not just because he agrees with me.
I couldn't agree more with Kim's assertion (which I'll restate) that fairness is paramount in the tax system. Having a progressive but evenly applied tax rate makes tremendous sense. I can't speak to what the end resulting tax rate would be, but having it be evenly applied to everyone would make a world of difference.
While we're changing everything, I have mixed feelings on "income" tax for corporations. Despite the idiocy of our current supreme court, corporations are not "people". They are a organization of people for the express purpose of making money. Why are they taxed on their income? Why not tax the shareholders on the corporation's income at the time it occurs, as one does in a Sub-S Corp? If we did this, I can guarantee that corporations would be much more responsive to shareholders. The counter argument is that corporations need to have capital to use (which I agree with) and that they should be taxed on the creation of profit which is retained by the corporation and used as capital. But this argument doesn't make sense. Shouldn't the shareholders be taxed on their profit when it's made? If they then choose to leave their earnings in the corporation as capital, then they are "investing" after tax dollars. Of course this raises the entire discussion about tax on profit from labor vs tax on profit from capital.
I believe that what actually happens is nothing like the rational proposal Kim has made. What happens is that those who gain power tax those who don't have it. We have not progressed at all from when the Barons taxed whomever they pleased in any way they wanted. We have, of course, substituted the whims of a Baron for the whims of a Congress. But I've no evidence that anything different is actually happening. Those with power tax those without it as they please. In a republic like ours (do keep in mind we do NOT live in a democracy but a republic) the "power" winds up in the hands of those who we've elected to represent us and in those who support those elections most aggressively.
Finally, as to the various middle-class deductions (like mortgage) I think most tax payers would be thrilled to get a 30-40% tax cut in exchange for giving up all their special little loopholes.