Will Fly wrote:

"And what political arena am I entering when I play a 3-part slip jig at a session?"

In the narrower sense, none. In a broader sense all musical activities are political. I would argue that by taking part in a session that are making a broad political statement.
You are saying "I am playing here without being paid. By doing so I am abandoning the mainstream music industry that would seek to control manufactured recorded music which is geared to producing maximum sales whatever the quality of the output".

You are also saying, "By playing traditional session tunes rather than the conservertoire music that