I'll second the explanation above; it's a good one.
People aren't tools -- or, if they are, so are you. Tools using other tools.
Treating others as you would like to be treated yourself generally is a good way to go, although it's certainly not all-inclusive and you also have to try to take into account things that you know about them (or the possibility of things that you may not know) which might result in them wanting to be treated in quite a different way in certain situations. But when it comes to the very core of how to treat people, it works: people don't want to suffer, just like you. People want to be happy, just like you. You don't even have to fully understand it to have at least some level of compassion (although it helps and deepens it to try to understand it as well as is possible for you) but without people having that compassion, we'd live in a very unpleasant world, much more so than it is now.
There are a few different ways it's possible to look at it. One is that of each person, each life being a story. And being born into your body and living in it (with all the personality traits, identity and such which are tied intricately in with your physiology -- your brain -- and your particular experiences to life) is just like reading a book or watching a movie from beginning to end, except unedited and with the choice to change how the story goes by consciously engaging with and directing it in different ways.
You could just as easily have picked up another book (who knows? I don't know if there is such a thing as reincarnation, but there are some who quite literally believe that you will eventually experience being every being in this universe, in which case it would pay to be kind to others in the most literal sense. Even if this is not the case, though, it still pays in another way.) Generally good people want all those books they come across to be as free of pain and horror as possible, and full of some joy -- granted, people tend to be particularly invested in their own books, but it sometimes helps to try to be less so, both in terms of making others and oneself happier.
Sorry if this is difficult to understand. But believe me, if you can spend some time considering it and understanding it at least a little more, it is worth it. If only as a theory, if you cannot feel it. Even if we are all tools, even if we are all emotionless and suffering and joy are only settings, it's in all of our best interests to treat each other as well as possible (in which doing our best to understand others is instrumental, even if we cannot do so perfectly) -- we can build better things, be of more use, and get to much better places.
Last edited by sparrowblue on 06 Apr 2015, 8:32 am, edited 2 times in total.