The percentage doesn't matter. You have to pay taxes on the stock you own (ie, your startup). You do that by selling the stock. As the value of the company increases, you are forced to sell off increasingly large chunks of your stake to pay the bill thereby loosing ownership (control) in the process.

With an estate tax, the value is assessed once, I'd assume (at death/inheritance), then due to be paid. You might have to sell of a third or whatever of the fortune/company, and keep the majority.

Sure, over successive generations, the family might lose control of their original fortune/company, but that is compatible with the intention of the tax.

You'd lose control much, much faster than that at the sort of rates being proposed. Even 1% per annum would destroy control well within a career, let alone a generation considering exponential growth.

edit: Just noticed that you are talking about estate taxes and I'm talking about wealth taxes...