Image that the economy is a field of wheat. It grows bigger every year as workers become more productive and learn how to fertilize and water more efficiently. At the end of the season, everyone gets a chance to head into the field and collect some wheat.
Some people don't have any tools. They pick the wheat by hand. Others have managed to fashion scythes and can collect a little more. But, the kid who inherited $10b has a fleet of combines that race into the field and collect 75% of the wheat in a flash.
The economy (wheat field) grew bigger and everyone had a little more wheat but the $10b kid got way more than the others and can now buy another combine for the fleet to get even more next year.
Without some rational tax on inherited wealth, we will create (and already have created in the United States) a plutocracy.