That relationship with the servers, by the way, also has a name: it's a principal-agent problem. Servers have competing incentives: to serve the interests of customers (better service) or the business (reduce ongoing costs). Tipping shifts the incentives around. You could attempt that shift with other mechanisms, like after-dinner surveys, but you know how well that'd work.
It costs time, effort, and money to provide better service, so I'm not from where you get the moral dimension of having to buy them. They have a cost; of course you have to buy them.