As noted above, the high tax rates were effected to pay for WWII and the Korean War. I'm not sure how such a policy was justified to the taxpayers, but I'd guess it was seen as a reasonable sacrifice in a time of national emergency. I believe the estate tax was also implemented to pay for WWII, as well as a tax on excess "war profits" of corporations.
I don't think 90 percent rates would be justified today, but it does seem unusual that the only people called to do significant sacrifice are those in the military and their families, and those who rely on government programs falling to budget cuts, while the $2000-a-plate crowd gets new tax breaks.
Of course, these are different times.