It's become a bizarre cultural norm. I feel it makes for a master/ servant relationship, rather than mutual respect for someone doing a job, and someone buying a service. Very inequitable. A tip is something that should be given willingly for good service. That is no longer the case in North America from Canada, the USA and Mexico (in tourist areas). It's invading places like South Africa (as mentioned above) and Bali. It's quite a scourge but it's so ingrained now there is really no way to get rid of it. Some might argue it creates better service but really who wants to have something over someone to get that service. I find it quite uncomfortable.
My take is you need to be careful saying "it's become a bizarre cultural norm" when referring to the US or Canada. It definitely has not "become" anything as it's been a part of the "cultural norm" for a long, long time. This doesn't mean you have to like it and I certainly agree that it is bizarre that it now permeates in certain situations here and in other territories.
However uncomfortable you find it, saying that a tip should be given willingly for good service then noting cultural norm means that you don't understand life in service industries in the US and Canada.
Please note that this is not a personal criticism - it's just how things work. In almost all cases the service will be efficient and friendly not because they expect a tip but because that
is the cultural norm - big smile, friendly greeting, you're welcome after every interaction and every other aspect of service. Not in all cases sure, and if that happens you can show your displeasure with a low or no tip.
For clarification, in the 80's when in my twenties, I worked 5 ski seasons and summers in Vail CO. My job was working in the only late nite diner in town. We took the order, cooked the food, served the food, and gave the customer the bill at the end of the meal. I got paid $4 an hour but made good tips on a busy night. So a 40 hour week gave me a small fortnightly wage but the tips were what i lived on.
By all means let's not allow the culture of tipping to take off here any further than it is at present - please! But complaining about what happens in a "culture" with completely different "norms" is not really valid.