The part you still don't get, NowhereM, is that the vast resources held by America's wealthiest has little effect on their lifestyles whatsoever. They're beyond the saturation point. Beyond some point or another, money and resources aren't about wealth at all, but about power, power over the rest of us.
I think it's also important not to set the exemption wrt estate taxes too low, because it'll kill middle class aspirations and damage whatever reserves middle class people have.
Inherit several million, have it made for life by the standards of most of America? Fine- because you have no power over me or others. Inherit vast sums, make more money than some small countries w/o lifting a finger, buy and sell politicians as if they were pet cats, finance think tanks and foundations to influence the thinking of the nation and the world? I think that needs to be reserved for people who've earned the money themselves, even if I might disagree with them...
Extreme concentrations of wealth via inheritance lead to oligarchy, whether that be the titled nobility that once ruled europe or the families that run south and central america. Constructive re-allocation of resources ceases, because they have excess resources in the first place. Human society has traditionally had ways other than taxation to correct that when it happens, usually war and revolution. Tear it all down, start over. America is very myopic in that respect, because we're a very young society. If we want to avoid the inevitability of undesirable solutions that cyclical over concentration of wealth has wreaked on other societies throughout history, we need to prevent that concentration in the first place...