Look at it as a regular income event. You were taxed when you got that money from whoever gave it to you and now your kids are being taxed when they get the money. Your kids aren't you. Money isn't a taxed-once thing, it's taxed every time it changes hands. Death is an event at which money changes hands (from you to your kids), and is taxed appropriately.

Anyway multi-generation estates are very well tested as being bad for society over time. Just look up monarchies.