The political principle is equally simple: government should, as far as possible, treat all its citizens equally. Politicians often talk about equality, but they seldom live up to its core meaning. A true egalitarian doesn't believe in affirmative action, because it means the government discriminates on the basis of race. A real believer in equality opposes heterosexual-exclusive civil marriage, because it means the government discriminates on the basis of emotional/sexual orientation. And such a liberal also opposes punitive or "progressive" taxation, because it means the government discriminates on the basis of personal success. If we get rid of different rates of taxation, and we're all taxed at the same proportionate rate, the successful and hard-working still pay far more into the public coffers than the unsuccessful. They're just not penalized even further by a higher rate. If you want to help the poor, and we should, then we need to focus government spending on programs that help the under-privileged. We should boost educational standards in state schools; provide effective welfare that leads to work; ensure good healthcare, and so on. But there's no need to penalize hard work and success. Or to defend inequality, on the basis of envy.