TheSession.org isn't always vitriolic about guitars at sessions, though there's a certainly a lot of heat on the subject - and many other matters. TheSession is also dedicated, so they say, to mainly Irish and Scottish music. I go to mixed sessions, French sessions and others, but always avoid those whose musical ears are blinkered.

It doesn't matter what you bring to a session as long as you, a stranger, listen to what is going on and try and fit in. A session is a great way to learn new tunes and to contribute to a good musical evening - and to have fun. I play guitar, tenor guitar and mandolin at sessions. Mandolin is great for picking up tunes quickly and joining in melodically. Tenor guitar, being tuned in 5ths (like a viola) is also good for this, though some tunes based on fiddle music can be a little out of the playable range sometimes. As far as guitar is concerned, the emphasis for me is not on laying down solid chords all the way through all the tunes - unless that's specifically required - but on providing some subtle bass line and harmonic support. You need good ears - but you need good ears for any instrument.