I do not think there is a clear distinction between right wing and left wing conspiracy theories, both are often expression of a certain brand of populism that claims fantastic plots without a shred of emprical proof. There is, however, a difference between such claims and the research on social networks to identify human actors with names and adresses behind the workings of the system (see for example the work of Beth Mintz, _The power structure of American business _, Chicago : University of Chicago Press, 1985.). But exposing human agents behind social systems is not the same as conspiratorial views: the former emerges from a careful study of personal constact, exchanges, dealing etc., while the latter is an apriori assumption about how the world operates with little or no empirical support to back it up. Stated diffrently, the empirical search for human agency aims to identify secret networks and dealings among other social institutions and intractions, whereas for conspiratorial theorists everything is a conspiracy.
I do not think anyone of us really knows the whole story behing JFK's death, so the lone gunman theory is as good as a rightwing conspiracy theory. Both are plausible, but we canot rule either one out.
My only problem with the conspiract theory is why would right wingers want to eliminate JFK? You do not suppose he was a closet leftie, do you? He was pretty right wing (more so than Clinton) and pretty corrupt as well - so if the rightwingers wanted something from him that he would not want to give, they could get it by threatening to expose his sex scandals, mob connections, etc. just as they did it in Clinton's case, except back then it would have had a much greater public effect. Pressures, blackmail, backstabbing, character assassination are more effective political tools than actual assasination. A corrput, vulnerable president is certainly more pliable than a dead one.
wojtek