Tipping is a complicated subject where I feel a lot of people are myopic and limited to their regional worldview.
In North America (US and Canada), tipping is not legally mandatory, but it's so ingrained that everyone, including poor customers, is expected to tip. Waiters make wages so low that they rely entirely on tips. Poor customers are entitled to the occasional treats, but should it be at the cost of a waiter possibly being stiffed? I wouldn't think so, but I can see disagreements there. That said, in NA, since tipping is so ubiquitous, customers are basically trained to include tip as part of the cost. I can scarcely imagine someone looking at a menu and going "hmm I can afford this, but only if I leave out the tip". I don't think this scenario is very common, and I think most people who don't tip do so because they're jerks/penny pinchers rather than poor, but maybe I'm wrong. If studies are done that show differently I'd revisit my views.
But then you have waiters who will defend the tipping NA status quo, because they happen to thrive in that system, and make better money than they would under a regular minimum wage system. And frankly, it's true, in my experience, that service is overall better in NA. That's very likely because waiters have to "earn" their tips and are forced to be nice, whereas in Europe they are "getting paid anyway, don't care if you're mad" (slightly exaggerating and generalizing, but you know what I mean).
But, on the flipside, another aspect of tipping that is often overlooked is how PoC waiters get the shaft the most under tipping culture. I remember reading articles showing that black and brown waitresses get fewer and cheaper tips than white ones, which is really awful.
So, is tipping culture in NA fucked up? Massively, yes. Is it the fault of the waiters? No. Are you a moral crusader sticking it to the man by refusing to participate in this system? Fuck no. You're fucking over the waiter, doubly so if that waiter is a PoC. Are you an asshole if you don't tip in NA? Yes, very likely so.