I am "that guy". I worked in the restaurant industry for my first job, so I do know what it's like to live off your wages + tips. I, however, do not feel sorry for those people who have never developed a skill that will get them a better job. If I paid everyone extra for doing their job just because they make a low hourly wage, I wouldn't be able to afford food myself. In the restaurant industry, tipped employees typically make higher hourly wages (after tips) than the people preparing food and/or working other jobs. If they don't hit minimum wage, the employer is required to bring them up to minimum wage. I do typically leave a tip because it's (stupidly) expected, but I see no reason to blanketly tip some arbitrary percentage.
I don't care if my meal is $5, $10, or $50. If the service is good, I will tip $1-2 per person at the table and I'll be agitated while I'm doing it, because it's utterly insane for me to pay someone else's employees just for doing their job correctly. I don't expect you to tip me for properly fixing your computer--why should your food service job be any different?
I do leave a tip because it's socially expected, and I got tired of hearing people bitch at me for not doing so, a la Reservoir Dogs. I don't leave ridiculously large tips or "20% of the total meal" tips because I think it's stupid that a person serving me a more expensive meal automatically receives a larger tip for doing the same job as a person serving me a cheaper meal.
I used to tip delivery services well. When pizza and other places started charging a delivery fee, that took the place of tips, so they get $1-2.