I agree to a point - but I can name jobs where tipping is expected - like delivery drivers. Why should I tip the Jimmy John's guy who walks my sandwich two blocks to my workplace (I do tip him, BTW), and not tip someone who has worked very hard to make a member of my family clean, comfortable and happy?
Bellhops, delivery drivers, valet attendants... I don't understand how tipping them is expected, but someone who has to groom a dog (which requires much more skill and endurance than driving a pizza to someone, or driving a fancy car to a parking lot) isn't counted in the "common courtesy" tipping bracket. (And yes, I do still tip valets, bellhops when I have the occasion t use them - and I always tip delivery drivers)
IMO if someone is performing a service directly to me, a service that takes a significant amount of time - they get a tip, however small it is. My mechanic gets tipped when he changes the oil in my car, the tow truck driver got a tip when he had to wrestle with my car - on a Sunday - when the transmission broke, and if I took my dogs to groomers... they'd get tipped, every time.
I've worked enough service fields to know that people like that are overworked and underappreciated (and often severely underpaid)... so anything I can to to let that person know that I'm thinking of them, and appreciate what they've done for me, I'll do it. This isn't always money - often times it's me being lenient about a service, or not freaking out on them when they make a mistake... and it's gotten me a lot of things I didn't used to get.
I don't get charged for extra cheese at Jimmy John's anymore. I don't get charged for queso on my Flying Burrito anymore. I get an upgraded oil change for no additional cost. I get employees that are genuinely happy when I walk in the door. And to me, it's worth it.