There are many things I dislike about tipping:
(1) It is expected. Some places even tack on a mandatory gratuity automatically. In this case, it defeats the purpose of the tip - extra given for good service; treated as obligatory it is simply a default cost to be added without some judgement, which defeats the purpose of a tip. If this is the case is not a tip at all and should not be called that at all; it is a fee for labour, not a tip, and this should be clearly labelled before anyone buys something. There is no reason to engage in the euphemistic language other than to obscure what is really going on.
(2) It is arbitrary: some services expect one, others don't. In high school I loaded cars at the grocery store outside in the cold, laboring hundred of pounds for hours: no tips. But those inside bringing a cup of coffee expect something. Indeed, one can see a 'tip' section in a buffet where the staff don't do any traditional restaurant service that warranted a tip. All this talk about what % is arbitrary too. 20 percent, 10 %. So, If I buy a cheap meal with 3 courses to serve I should tip less than if I buy one plate that is more expensive? How is this supposed to make any sense? Business should state the entire cost upfront so people on tight budgets can make a predictable plan. Tipping seems to easy an excuse to not pay the workers a wage that reflects the cost of the service, to avoid paying things like vacation pay or workers comp or payroll taxes in countries where a business must pay these as a function of employee salary.
(3) No account for costumer wealth: I worked jobs when in university that received no tips and payed less than a restaurant server would make per week. Every dollar I spent was accounted for. I am surly not going to add another 20% on my bill in this case without very good reason. Many people might go on a dive vacation only after scrimping and saving for a year or even more; their budget may be tighter than the workers on the boat. Not everyone is part of the leisure class going on holidays with a trust fund back home (I suspect the history of tipping derives from a time back in the day when only the uber-rich had any time or money for travel). Just because someone is on a dive trip or in a restaurant does not mean they are loaded with cash to throw around.
(4) Dodgy politics: there are lots of articles in the newspaper in my country about dodgy schemes with tips: the employers taking a percentage, or pooling all tips to be distributed amongst the entire staff (hence my tip is not going to the person who gave the extra special service); indeed, some places require the wait staff to add money to the tip pool based upon the value on the receipt, even if the client did not leave a tip.
That said, if I am flush with cash I am not averse to adding in a gratuity if the service warrants it; some of the workers are, like I was, cash poor and getting a few extra dollars would have a high utility; but claiming a tip is obligatory or claiming that some amount is obligatory is ridiculous.