Steve Shaw
And it [tunes from tune books ] taught me precisely zilch about active listening as I learned, the need for flexibility, the subtleties of rhythm and how to vary and ornament tunes. So I have every idea, you see.

No, it shows that you have absolutely no idea. Music notation, at least in folk music, doesn't set out to do any of those things any more than the text of Shakespeare teaches you to act.

A 6/8 time signature at the front of a jig, for example, conveys a mechanical notion of something that is as un-mechanical and fluid as can be.

No. It tells you it's in 6/8. If to you that means mechanical, then that is how you will play it; if you think it means fluid then play it that way. That is up to the musician.

A 4/4 time signature in front of a reel gives no hint as to the potential for playing the tune with a bit of lilt.

Of course it doesn't. That comes from your experience of how reels sound.

Anyone who even thinks they can notate a slow air is nothing less than a scoundrel.

Anyone who thinks that you should slavishly follow the notation of a slow air is never going to amount to much as a musician.

I honestly can't understand why anyone would want to deliberately put such obstacles in their way when they could learn tunes by hearing them played.

The notation puts no such obstacles in your way, they're all of your own making. You seem to have chosen to be straightjacketed by the dots. You seem to have decided that if you learn from notation you have to stop listening. No wonder you didn't get much from it. By rejecting tune books, you have cut yourself off from a vast treasury of music. Do yo regard O'Neill's as the work of the devil? Your loss.