Some people would say not to help these people. They would say that you are a "friendly helpful person" or "M&S". This is simply not true. When you are helping a friend, you are making an investment in that person. By helping these people, you are making them better players (usually). They will appreciate it and it will make you feel good.
WoW is not a game of black and white. It is all blurry and mixed. Just like there are two factions who are neither good or bad, there is a blurry line between good and bad for players.
You may have a person in the top raiding guild on the server in full Ulduar 25 gear who is terrible at PvP. You can have someone who makes ridiuclous amounts of money who just can't get out of the fire. There are several ways that people can be good or bad.
Good and Bad are both very vague terms as well. What is good to one person is bad to another person. A 2100 rated pvper probably thinks someone at 1700 is bad. Someone taking on Algalon probably thinks anyone who has not cleared Ulduar 10 to be bad. Of course this is not true. These are just generalizations by people at different points in the game. The scale of "good" and "bad" has a wonky slider that changes enormously from person to person.
When you help your "bad friend", they will become your "good friends" and likely help you down the line. This could be in the form of instance run throughs or even gearing up your freshly dinged 80 toon. People who think that spending time on people is a waste of time are a waste of life. Investing in people is one of the smartest things that you can do. There is no end to the profits of friendship.