Supply side is actually not the issue here. It's the old ethical debate of Who Pays What to Whom. And all that is is a debate about first principles, not tax rates. The only thing we can do is watch and see how Bush's tax relief package plays out. However, having not read the WSJ piece, I can only go so far in this debate and do so with any shred of intellectual honesty.
As to Russia, Putin put in the flat tax precisely because there is a culture of tax avoidance, fraud, and scam. If you lived under Communism for seventy years, you'd learn all the tricks, too. The thirteen percent deal is low enough to be fair to the workers, while moderate enough not to hurt the Mercedes Benz people.
Be Seeing You,
Chris