While you have a point, and it should be noted that the US government has never been able to tax more than 20-22% of the nation's GDP (not even in WWII), there has been a sea change starting with JFK in taxation policy towards "the rich". The history of top marginal Federal income tax rates is (memory plus http://www.ntu.org/tax-basics/history-of-federal-individual-...):

Peaked at 77% during WWI.

Down to 24% the last time Republicans ran the economy (down and up a tick as engineer Hoover tried to fix the economy :-( ).

63 then 79% under FDR pre-WWII.

Up to 94% during WWII.

Never got less than 82% post-WWII, and "We like Ike???" after he kept Truman's 91-92%.

Then down to 77% under JFK in the first supply side tax cuts.

Bounced between 70% and the mid-70s LBJ through Carter.

Down to 50% Reagan part I, then down to 28% after the great tax rewrite in '87.

Raised to 31% by "kinder and gentler" Bush I and to 40% under Clinton.

The devil 'W' reduced that to 35% ... where it's stayed, even under Obama and Democratic legislative super-majorities.

We also need to factor in that inflation pushed people into higher tax brackets until Reagan, and capital gains taxes have never been indexed for inflation (nice racket, the government inflates the currency then taxes you for merely running in place).

One should also note this is intended to change people's behavior. The lower the max marginal rate, not to mention the capital gains rates, the less people focus on tax advantaged investments. I watched my parents change their business strategies quite a bit from the '70s to the '80s, and in ways that ... trickled down a lot more.