Why is taxation of income not expropriation?
If taxes act as disincentives, what incentives are implied by taxing income and not taxing holding wealth?

John Stuart Mill argued that unearned income should be taxed. As a result, he advocated taxes on gifts and inheritance (let's remember that the inheritance tax is on the receiver of the property, not on the giver - who is free to dispose of it without paying taxes). He also advocated taxes on residential values on the argument that ability to pay relates to disposable income of which the size of one's dwelling is a good proxy.

We would be rather better off policy-wise if we followed the ideas of late 19th century English liberal patricians, which means politically we're somewhere before 1850...

tens of millions of people stand to see their lives ruined because the bureaucrats at the ECB don't understand introductory economics -- Dean Baker