"A heavy progressive tax upon a very large fortune is in no way such a tax upon thrift or industry as a like would be on a small fortune. No advantage comes either to the country as a whole or to the individuals inheriting the money by permitting the transmission in their entirety of the enormous fortunes which would be affected by such a tax; and as an incident to its function of revenue raising, such a tax would help to preserve a measurable equality of opportunity for the people."