It's not moralistic. It's "worth" in the sense that how much marginal revenue that person produces. If you have to pay someone to sell $9 worth of coffee an hour, they're not "worth" more than $9 an hour, regardless of morals.
Then the store should change their prices, or perhaps close. If everybody is paying the same overhead (like staffing all day when they make money only during peak hours) then competition will operate as normal, prices may change to reflect costs etc.
Staffing is more complicated than "how much they sold during their shift"?
Sure, they'll try and pass off the costs to their customers. But with a higher price, there will likely be less coffee sold and less employment regardless.
Yes, staffing is more complicated, but min-wage labor cost for a restaurant are a significant portion of the costs and profit margins are very thin [0]. Many won't be able to absorb a ~50% increase in labor cost.
All will have the same labor costs. Minimum wage has gone up before; there are still coffee shops.
Its easy to play 'dot-to-dot' with these things - higher cost means lower sales means people fired. OR more money in the working class pocket means more coffee purchases means more hiring. You can connect-the-dots lots of ways.
The truth is, some of everything happens, and then it settles down into something workable. Yes we'll pay more for our coffee, but we'll also have more money in our pockets. And so on.
Staffing is more complicated than "how much they sold during their shift"?