No one earns a billion dollars. By that point you aren't "earning" money anymore. Tax it 99% for all I care. You or someone else should be spending that by thatpoin. If you're a multi-billion aire then that's rough, but o don't think your QoL will be impacted.

Also, your loins did hot "earn" that money either by popping out of a uterus. Inheritance tax is probably the easiest to push of you can convince people that children aren't entitled to be billionaires by existing.