It seems to me that capitalism discourages that behavior. If the system is setup to be transactional, and you can't rely on others reciprocating altruism if you need it; then it seems like engaging in altruism would be for suckers.
True-ish. But in older-fashioned communities - long-term stable, extended families usually present, participation in many altruistic groups and activities are established norms, everybody's noses not buried in web browsers and smart phones - there's this thing called "social capital". And, as a generality, it's at least as important as the monetary kind.
True-ish. But when you say 'older-fashioned communities' I have a feeling you are speaking through nostalgia or a rose-tinted view of an idealized past. Can you name some of these older-fashioned communities that exist today, and how they are different from the ones you are contrasting them to?
capitalism is so that strangers with no reason to cooperate can via the market. It should have nothing to say about you network or closer relations and how you interact. Altruism has a large place in life but in general it is directed to friends and family then your larger social groups.
Nit: That's not the defining property of capitalism. The defining property of capitalism is that the means of production are privately owned, as opposed to e.g. market socialism.
