As I understand it accompaniment or backing of tunes is a fairly new phenomenon (or however you spell it) and apart from maybe some dance bands, dates back only to the early recordings made in the US in the early part of this century. Aparently there was a strong musician's union around New York at the time and solo performances were against the rules, so most studios had 'house' musicians usually pianists but occasionally guitarists to accompany the solo players. Some of this was very unsympathetic indeed particularly some of the Piano stuff.

Ceili bands which mostly emerged it seems in the 40s/50s had piano backing and drummers, but not many guitars. A lot of 'traditional purists' think of traditional music as the stuff they heard when they were young, so ceili bands were fine (and traditional) - guitars were not. Many of the early attempts to accompany traditional dance tunes (e.g jigs and reels) were done by not very expert guitarists and didn't sound great. A friend of mine told me that in the early 70s if you went into a pub like O'Donohoes in dublin and you were able to play a barre F Chord you'd be thrown out for trying to be too fancy (an exageration but an indication that the standards were not all that high.

There were several high-profile rows and arguments between people who came to trad music via the folk revival (known as "the ballad boom" here) and those who came from a more trad perspective (known as the 'purists' which is a word I don't particularly like because it is used by many as a term of abuse. A lot of the anti- guitar sentiments come from that era.

New ground was broken in the late 60s and early 70s when bands like the Johnstons, Sweeny's Men, Emmet Spiceland, Planxty and the Bothy Band arrived on the scene. This music was more often termed folk music than ballads or traditional and you tended to get a mixture of songs and traditional tunes accompanied by various stringed instruments including guitars, bozoukis, mandolins etc. A whole new generation of 'Traditional' groups emerged from this. The groups were traditional more in the sense that their material came from the various traditions of these islands rather than that the format of their playing was traditional. The notion of a group of musicians sitting down and playing as as ensemble was probably pioneered, at least in a commercial setting, by Sean O Riada's Ceoltoiri Chualainn many of whom later went on to form The Chieftains.

The advent of guitarists who played the tunes and came up with innovative but senstive ways to accompany the music in more recent years has tended to lessen the prejudices in this area and guitarists such as those mentioned in the initial post here have blazed a trail which the rest of us can follow. To my mind something isn't bad just because it didn't happen 30 years ago - its different, but if it works it works. I must say I feel much less intimidated going into sessions with a guitar case than I did a few years back - part of this is to do with self confidence, but I think most people associated with sessions nowadays acknowledeg that a guitar in the right hands can add something to a session. Any instrument in the wrong hands can mess one up.