The upper class can absolutely afford to pay their taxes, but I don't see any reason why the tax rates need to be different. To make one taxable group favored or charged more than another is a type of discrimination, plain and simple. An even tax rate of 10 percent out of all yearly income would be reasonable.
Everyone should pay an equal percentage of tax, that seems fair. And I don't see why the rich should pay less as they supposedly have more money in the first place, so if anything, you'd expect them to pay more tax. I am not suggesting the rich should pay more tax but that would make more sense than to have them pay less.
Since there are DEFINITELY diminishing returns on income and their affect on lives. The most convincing argument I've heard against this is that taxes on the wealthy remove money that might otherwise have gone to investment (for the long-term benefit of the country), but if it comes down to choosing to tax one group over the other, improvement of infrastructure takes a back seat to the improvement of the lives of the less economically fortunate.
The money in the Middle Class is MUCH more spread out than the rich peoples money. As such, if the government started raising the taxes on us and not the rich, the rich would get MUCH richer. You would also see a drastic drop in free population. So many people would lose their money, and become a homeless person who can't afford anything.