National minimum wage does not make sense because cost of living varies per state; so small buisness would get hit hard in some states. Now, if Amazon wants to pay $15/hr nationally then good for them!
Those small businesses that would get "hit hard" by a $15 minimum wage? We're indirectly subsidizing those businesses with our federal taxes; those businesses are value-destroying enterprises.
(Edit: It's not just small businesses getting this taxpayer subsidy. Walmart and other large employers similarly transfer wealth from taxpayers to their shareholders by relying on government welfare programs to allow their employees to continue to do their jobs. In a very real way, Walmart dividend checks are paid in part by US taxpayers.)