Well, I rarely tip unless the service is fantastic. It isn't because I can't afford it , it's because I simply don't want to.
The restaurant corporations want us to pay their waiters/waitresses wages so they don't have to. If these workers have agreed to work for low wages that is between them and their employer. It's none of my business! If I'm supposed to pay 15-20% extra to cover their wages, why not add it into the cost of the meal?
For one thing, it lets you reward good service.
Take pizza drivers for example: They provide their own vehicle, their own gas, etc., and must maintain a good driving record, as well as be intelligent enough to learn maps, areas, etc. I worked as a trainer for a national corporation in the metro DC area, and I will tell you that maybe 1 out of every 20 applicants were able to do that work. They work for minimum plus tips. If you don't want to tip, go pick it up yourself. If you get rude service or cold food, don't tip and make a phone call. (Trust me, management can cull out the scammers, and they are anxious to correct a problem.)
If I can't afford a tip (or just don't want to leave one), I will hop my happy little self into the car (or taxi), go to the grocery store, and buy food. Cans don't require refrigeration.
I've seen sales slump over a mere 3% increase in prices. I could imagine what would happen if one company decided to do the "right thing" and raised their prices by 20% to pay more. They wouldn't be in business very long.
Now, I was very good at what I did, and I was paid very well for it, as well as getting a lot of tips because I was good. However, the average person working for tips is not capable of that, and the ones that are leave because of lousy tips.
Now, I for one, was diligent enough that everyone always got my best effort. However, for the most part, waiters, waitresses, pizza drivers, etc., remember lousy tippers, and your service will be provided accordingly.
If you don't want to tip, please stay home.
Edited to add: Tipped employees have to report tips. If you don't, you will be audited. If you're audited, the IRS will go into the computer records (or written records) and will charge your income tax based upon 20% of the sales you served. Too bad cheap tippers don't realize what the IRS does.