That's no more or less absurd than any other slightly unusual hobby. It could be stamp collecting or building model railroads.
I don't see what's absurd about it at all. I'm interested in Social History, that's what interests me in life, and so surely someone who's interested in that sort of thing would be interested in obscure left-wing political groups and stuff? I mean if you went into a history department of a university, and saw them studying crop rotation records from 16th century shropshire, would that be considered absurd too?
There's also another facet to this, which is socialsts of my generation are faced with a real problem with where they should devote their energies today. The Labour Party is a no-go. Been there, tried that, failed miserably. Left groups? Hopeless. Embittered and sectarian, wedded to a view of the world which belongs in the 1920's. UKUncut and Occupy? Far too liberal, far to peacable, and detached from any serious, long-term, political project. Anarchism? Every bit as sectarian as the standard left in my experiences, with exceptions. I also don't believe it's actually possible to destroy the mechanisms of neo-liberal capitalism without having a huge amount of power, the ruling class won't give up without a fight y'know. I have this horrible feeling that the horizontal loose networks and federations of sovereign individuals would be smashed to pieces by the forces of capital and the state if they ever got into a position where they do pose a threat. There's a reason the only "successful" revolutions in history have been highly disciplined, heirachical organizations, because something like that might be what's needed to destroy capitalism and overthrow the state. It's also the reason why pretty much all the attempts at revolutionary communism have, in practice, ended in failure and bloodbath. So I don't think there's an answer along anarchist lines either.
It puts people like me, and other young (under 25 if that still counts as young) socialists in an awful position. We're gonna have to begin the long, arduous process of re-established new ideas and new organizations to carry those idea's out into the public, as the generations prior to us have preferred to live in total denial. A working knowledge of where organizations have failed in the past would no doubt help in avoiding those mistakes in the future.
It's also pretty funny too, some of the crankish stuff i've heard these left wing groups get upto deserve their own sitcom.