Who tells musicians that they can't play along?? You can actually read, can you?

According to you, you do. This is what I actually read. You wrote it:

As for sessions being open, our session is our session and we more or less get to decide who joins in.

Zero tolerance for these talentless, insensitive tossers is the order of the day

We already have a guitar player and we wouldn't want two at once

I say again, it sounds like you're playing in a band that has a regular gig. Why do you call it a session?

AND:
The tunes are everything in this music.

Well, except for the guitar, the drums, the bass, the synthesizers, the singers, the rhythm, the harmonies, the chords, etc etc etc. You seem to be defining "this music" according to your own tastes. Fortunately, there are thousands of people all over the world playing "this music" in ways that apparently would give you a heart attack. And the good news is that it's all traditional playing, in that modern traditional players are doing all these things. Your comment about the bodhran being only 50 years old makes it sound like you are unclear on the difference between traditional music and historical music.