I would dispute the notion that the ‘concept of social capital’ is ‘fashionable sociological analysis, though it may be to the Conservatives (in which case it strengthens your overall argument that they are now moving into NL disursive territory.

The 1990s/2000s, woolly, trust-based concept of social capital is very much an appropriation of New Labour and its Putmanesque proponents of communitarianism , and harks back further to broad American pluralism. to that extent, I’m afraid Labour has only got itself to blame for its appeal to liberal rather than socialist traditions – you can see people on the left of the blogosphere who’ve fallen out with New Labour over this at http://communityconfusions.blogspot.com/2008/01/so-what-hell-is-social-capital.html

Perhaps what Labour/the left needs to be doing is rooting back further to the wholly different concept of social capital introduced by Pierre Bourdieu in the 1970s. Bourdieu sees social capital firmly n terms of power and struggle/conflict, and we need to reclaim the ‘concept’ in those terms, I posit. See http://www.istr.org/conferences/dublin/workingpapers/siisiainen.pdf for a handy review of the Putman and Bourdieu concepts, and an exposition of the muddled, atheorised concepts that Putman and co fiddled with,have handed down to New Labour and are now passing on to Tories.

As you suggest in your conclusion, it’s up to us to reclaim the concepts of socialism and thus clear ideological water.