>>-Estonia has a flat-tax system (smart!).

Smart if there isn't a wide range in people's finances. Consider someone making $30K/year paying the exact same percentage as someone making $1M. A 20% tax means the person making $1M doesn't buy that second yacht - and the person making $30K starts running out of food at the end of the week. The point of progressive taxes is that both pay the exact same on their first $75K or so. The $30K person never gets to a higher rate. The $1M one does.