They paid tax on the money they earned, they worked for it. This one time payment doesn't absolve their heirs from receiving the money in perpetuity without paying a single penny of tax on the same money in the future.

People get high and might and see it as some sort of double tax, inheritance tax is the price heirs pay for receiving money they didn't earn through their own means.

I'm not saying every penny should be taxed, sure have a threshold.However if you are 35 with no great skills and just waiting for a grand-parent to pass and inherit $/€/£3m. With the sole aim of buying 5-10 apartments and living off punitive rent you charge others who don't have rich grandparents, then you should be taxed to the hilt.