I don't understand social networking or how it can help me

I've been building websites for other people for a few years, however these have (for the most part) been small static sites which served only to give the business owner the most basic, minimal amount of web presence for the price.

However I recently started a community site - the main idea being a place where idealist people could put up a debate and discuss their arguments with other people. No one particular genre or subject - a general debate site open to guests and registered members.

My problem is I'm having a hard time growing this community. A lot of members have transitioned from another site which went under but this is not enough to sustain the site and most are slowly withdrawing from participating.

I've tried to integrate the site into social networks (twitter and facebook) but what little content gets discussed seems to remain solely in the domain of those social networks, which is understandable. People are inherently lazy and don't care for links.

The question is.. how on earth do social networks benefit me if I'm not getting any traffic or user retention from them? I'm just serving to promote THEM. Am I just wasting my time trying to make this work?

I don't understand the whole social concept at all.