In one episode of Community, the study group took over the supply of deep-fried chicken (in a mafia movie parody), and Abed was in charge of distributing it to the rest of the school. When told to stop, and that the mafia movie was over, he replied "I'm not doing a mafia movie. In fact, I don't need movies or tv shows to talk to people anymore. Before I only needed them because the day to day world made no sense to me, but now everyone's speaking the same language, chicken. I understand people, and they finally understand me."
Everyone has different terminal goals. Some people want to cure cancer, some want to win a race, some want to eat spaghetti, and some want to meet new people. This should make it very difficult for two people to interact and exchange goods or services, since they want different things and have no way of knowing what the other wants (short of directly asking). However, in capitalism, everyone shares one convergent instrumental goal, money.
Completing your terminal goal, whatever it is, is probably exceedingly difficult without money. This means that everyone needs money for one reason or another. This may seem bad (since not everyone can necessarily get money) but it means that everyone understands what everyone else wants, and it opens the door to interaction, cooperation, and trade.
Everyone understands the language of money. Just as making a friend with someone who doesn't speak your language is more difficult, trading with someone who is entirely uninterested in what you have to offer (or if you are entirely uninterested in what they are offering) is much more difficult.
If you produce lots of honey, and all you want is goats, then if I want some of your honey I've got to find goats from somewhere (figuring out what the goat guy wants in the process). Probably this ends up with you having only honey and no goats, and me having no honey. However, if I had money, and you could be assured that the guy with the goats wants money, then we can trade. All of a sudden trade becomes possible, I get honey, you get goats, and everyone's happier. Trade could only really happen when we both spoke the language of money.
Furthermore, when you meet someone in a capitalist society, that person represents an opportunity for fair, mutually beneficial trade, and should thus be treated kindly. On the contrary, when you meet someone in a world without money, where you're supplied with resources free of charge, that person represents a potential drain on your resources, and is thus a threat.
Capitalism unites people. It gives everyone one incentive, one goal, that everyone works together to strive toward. It doesn't matter that Joe wants blankets and Bob wants beef wellington, they both want money, and they both know that the other can help them get it.
This doesn't mean there wouldn't be crime, or incredible acts of immorality. There will always be people who choose evil, but in capitalism there are avenues for cruel people to get what they want in mutually beneficial ways. Some will decide that these avenues aren't economically favorable to illegal or cruel methods, but these passageways exist for the many who do decide that they are favorable.