Income Cap

My friend thinks we should cap people on making a certain amount per year, he gave $10M as an example, because “no one needs that much money to live.” I countered with the fact that business owners don’t just hoard that, they want to expand on their business, not to mention all the expenses they pay toward running it in general (i.e. paying employees to start). I have a hard time defending against “humanitarians,” but what they say doesn’t always make sense. Why?