The whole pro-death-tax argument boils down to penalisation of the successful.
If I eat beans and sit in the dark my whole life, saving up almost every penny I earn (and being taxed on it already), why shouldn't my offspring reap those benefits without the gubmint taking nearly half of it, for no other reason than that I'm dead?
Just tax live people to an appropriate level. Death tax is simply a disincentive to prudence and success.