Tipping is a mostly American phenomenon. In restaurant culture it becomes a legal loophole which allows employees to be paid less than the federal minimum wage. It is considered so compulsory that many restaurants' printed checks will include a calculation tool or even add a non-negotiable gratuity line item for larger parties.
Coffee shops aren't allowed this loophole, but tipping has still found its way into the café. On the surface, it seems like a nice way for customers to express how much they appreciate service. There is value, however, in a bit of critical thinking about this tradition.
A Strange Model
Consider first, how coffee beverage buying works. Most coffee houses have walk up cash registers as the beginning of the 'café experience.' In other words, you have to pay first. You experience giving someone your money before even touching or tasting any coffee!
Asking for payment up front always shifts power away from the customer to the purveyor. In any other practice, this tactic is used when there hasn't been trust established (often this is linked with non-existent credit), and the purchaser has to 'pre-pay'—an example is the pre-paid cell phone.
However, common sense dictates that the norm for commercial transactions is that they be finalized after a service has been satisfactorily completed, like when a bill arrives at the end of a meal. The café inexplicably operates more like a scorned creditor than a pleasant craftsperson. When this type of pre-payment also includes pressure to offer gratuity, we have entered a new realm of awkwardness.
The Tip Jar
Tipping is a peculiar practice no matter how it manifests, but it is especially unique in café culture. The quaint 'tip jar' is almost always at the register, which turns the normal food-service process upside-down. It makes it so you don't tip because of good service, you tip in hope of good service.
Offering extra cash to inspire stellar care-taking instead of rewarding it when it actually happens is a bit like buying a birthday present for someone to get them to throw a party.
Coffee Needs Liberation
Unfortunately, this tension has become so associated with coffee that it is difficult for anyone to imagine this particular craft in any other context. Many assume that buying a latte will be a customer experience on the same level as a visit to the DMV (often including the wait time!).
It should be obvious that there is room for disruption here.
One way to disrupt this model is to buy beans. Unless you ask the employee at the register to grind your coffee for you, there won't be any reason at all for you to feel awkward about simply paying the asking price and not contributing to the strange jar of money.
Also, you will be holding the product when you approach, resetting the scales of power since you are offering money for something you have already taken into your possession. Think of this as the Ron Swanson approach to coffee—very straightforward. Physically carrying something to a cash register is a surprisingly psychologically 'proper' experience.
Make Your Own Coffee
There may be a day when this model turns around but, until then, there is your kitchen counter.