First, one of the best ways to do social good is to fight capitalism. Just by working at a worker co-op, you're doing this. Many tech co-ops are also built around resisting other oppressions like racism, patriarchy, etc.
Second, many co-ops (e.g. http://sassafras.coop, the one I work for) work on lots of social good projects.
You know, don't want to think you actually think that. Perhaps you meant, "fight the negative outcomes sometimes found in capitalist societies."
Inequality causes capitalism. Liberty allows inequality. Those "negative outcomes" come from inequality, not capitalism. Fighting capitalism is a workaround. It's an appealing workaround because the "underlying system" is centralized, and inequality is not.
The negative effects of inequality are free to do harm in a society with capitalism. That does not make capitalism the cause of those effects, it simply means that capitalism does nothing to prevent them.
Socialism does (claims to) do some things to fight inequality, but that does not mean I must prefer it to capitalism.
Inequality does not come from capitalism. Liberty allows inequality. Those "negative outcomes" come from inequality, not capitalism. Fighting capitalism (socialism) is a workaround. It's an appealing workaround because the "underlying system" is centralized, and inequality is not.
(Personally, I believe market economy has been much more beneficial to society in the past than it is now - simply because it's running out of "low hanging fruits", and the disconnect between its implicit values and what humans would generally like to see is growing.)
Generally speaking, you need a certain level of material security to worry about more abstract things like social good -- or even sexual pleasure. Lots of stuff I have read indicates that people in wealthy countries have a great deal more sex and talk and think about it a great deal more than those struggling to get something to eat. It is something of a luxury good. Ironically, the complaints about being a member of the lonely hearts club is generally an indication that you already have some baseline amount of your needs met well enough to bother to notice what you lack in that regard. People who are poor or oppressed enough typically spend all their time worrying about resolving whatever their largest problems are and spend much less time thinking about things like love, sex or romance.
Maslow's pyramid and all that.
You're 100% right about the hierarchy of needs (and about my baseline need satisfaction too; I can bitch about the state of the world exactly because I have somewhat stable income, health, safety and social sphere). I'm not disputing that. But since there are people who have those needs satisfied and are free to worry about more abstract things, is it wrong for them to ask how can they contribute so that more people reach that level of Maslow's pyramid (or, alternatively, so that the whole world won't go deeper into shit than it already is)?
So, perhaps we should just let this be as we seem to be talking at cross purposes.