I'll never forget having lunch with my co-workers, all of whom were paying 30-35% in income taxes, lecturing me that a 20% capital gains tax was unfair because the investor, "already paid taxes" on that money when it was first income, so taxing the gains amounted to double-taxation.
I've never understood the argument that raising the capital gains tax would slow economic growth either. Why would people give up free money just because they have to give a little more back to the government that makes the marketplace possible?