We can assume they paid their taxes when they received their paychecks. Why should their heirs pay them again?
Because their heirs did nothing to earn the money unless we consider kissing ass a valuable skill. They essentially won the (genetic) lottery and they should be taxed the same as someone who won the Mega-Millions lottery. The source of the funds is irrelevant. If I gave you $1 billion today then you would owe taxes on it. Why should it be any different if we happen to be related?
So you are saying if someone should happen to get lucky that the state should take it away from them because it's not you?
It's not only the super rich that inherit things. Farms that have been in families for generations are being sold off to pay the taxes when the farmer tries to pass it to his children. These farms may have millions of dollars in the equipment alone so the state sees these kids as inheriting millions of dollars. These are not "lottery" winners. These are people that have worked a farm their entire lives only to have it ripped from their hands because of class-envy assholes like you think they are getting away with something. How 'bout trying to mind your own damn business for a change.