Yes, as I noted, a flat tax is very popular. And not just with the rich, but ordinary middle class folks like the idea too, as you can tell from the comments in this thread. Despite its popular appeal, a flat tax is a disastrous idea, at least as it has been proposed for implementation in the U.S.
European countries generally tax consumption rather than income, though someone here pointed out that some countries might also impose a very low flat tax on income as well. The devil is always in the details. The flat tax as it has been proposed by various persons running for public office in the U.S. would have disastrous long-range affects on the U.S. economy and its people! Be careful what you wish for.
Although the U.S. Federal tax code is an unmanageable mess, blaming the IRS for this is misguided. The code and the IRS are both creatures created by Congress. If there is any fault, it lies with Congress.
If it is not possible to fix both the Tax Code and the Government at the same time, then it is more important to fix the Government. Fixing the Government requires that the First Amendment by fixed. Nearly impossible I would think, as the U.S. is caught in a Catch 22 situation in which a well-working Government is needed to fix a malfunctioning Government. Perhaps, in desperation, a philanthropist like a Buffett or a Soros will step forward with billions to see that it is done. That is what it would take: a massive force outside of Government. I'll certainly be dead long before a significant transformation occurs. I still care however.