Minimum wage is the minimum for everyone, by federal law. The employer can only pay less if wage + tips < minimum wage. And that shit is pretty heavily enforced… when reported.
Problem is, it’s in neither the employer nor the employee’s interests for you to know this; they both prefer blaming the customer.
There are other minimum wage jobs that are not tipped. Servers and stuff whose wage is the minimum should accept that minimum wage, ask for better pay, or fight for the minimum wage to be increased (for everyone), instead of trying to guilt trip the customers into paying them more.