What proportion of posters on MN are right/left wing?
I think MN has a tendency to be more left, however as you say some threads look majority right-wing.
I'd say MN is fairly representative of the general electorate, but lefty people are attracted to certain threads and right wingers are attracted to certain other threads.
The general electorate is not majority right wing nor majority left wing. Most people swing depending on the issue.
(Actually this is why defining politics by left/right is problematically reductionistic when real life is so nuanced).