There are all kinds of irrevocable trusts that exist to remove assets from your taxable estate so that they can be passed to heirs without paying estate tax. Raising the estate tax (which is already 40%) would just make planning to use these techniques more attractive.
The existence of perpetual trusts is solvable in a world that has decided to fix the insanity caused by intergenerational wealth transfer instead of propping it up. "This thing we could also eliminate stops us from eliminating this other thing" is a silly platform. Just eliminate them both.