I never tip. Ever. First of all I'm too stingy for it; second of all, it's a disgrace that, in some (otherwise deemed civilised) countries, people are underpaid and expected to live of gifts, like beggars do. I refuse to help uphold a system that works that way. Third of all, most waiting personnel I ever met doesn't deserve a tip...
I hope you never visit North America, and if you do, please do not eat in sit down restaurants. I"m sorry that you don't agree with the culture of tipping, but consider as just that - a culture. If you are in a country where tipping is expected, then consider it part of the bill and just do it.
I can't really justify why we tip, and I can really only speak for Canada, but sit-down restaurants are just about the only places where a certain tip is absolutely expected. In this case you are paying for the service of somebody waiting on you hand and foot. So tip accordingly - give a good tip if the service is good, and leave a bad tip, or even nothing, if the service is bad. In other places, like bars, taxis, hairdressers, etc.. tipping is expected, but it's more casual, and is often just a round up of your bill. But if you get exceptional service from any of these places, than a better than average tip is appreciated, and noticed - the next time you come to the bar you will probably find you'll be waited on pretty fast. In MacDonalds or Subway tipping is never expected. Yes, the 15 year old serving you your BigMac would love a little more than minimum wage, and if he's treated you well then you can throw a little change in his jar. But don't feel its required.
I say all this as a waiter. Every cent that I've spent on my travels has been earned through tips. I am not a beggar - people choose my service and they pay me for it. The customer pays the restaurant for the food they are eating, but they pay me to treat them like gold and get them anything they want while they are there. If they don't want that service they are welcome to get take-out or head to subway down the street. If I give poor service then I expect a poor tips and I do notice a large dip in my earnings when I work hungover or I'm not in the mood to deal with customers. But when I'm on my game I expect to get paid accordingly. And I assure you that waiting tables is a job that no one would do unless the money was good. I also tip others accordingly - as a server I am a very critical customer, and if I don't get the service I expect, then they don't get the tip they expect.