It’s not about a level, it’s about the rule. To everyone who says “15% is fair,” consider what you’ll feel like at 70% marginal. Literal global rule. Some would call that overreach.
If you're at 70% marginal, it means you're already earning an ungodly amount of money
I say this to demonstrate that “ungodly” always means “more than me,” irrespective of all else. Justification through jealousy. A recipe for a lowest-common denominator society, at global scale.