Calling the income "unearned" doesn't make it unearned. It doesn't make people any less deserving of keeping what rightfully belongs to them.

At some point in the past, a person (possibly an ancestor) took risks to create wealth. Part of the motivation is to later have an easy retirement or to support one's children. You'd kill that motivation, causing people to avoid the risks which would no longer create wealth, and thus prevent things like start-ups.