I just ignore it Dick. As you say it is crap and the people who preach it just do it to wind others up. The prevalence of Anglo Concertinas historically in the west of Ireland is, I believe, largely because they were cheap. Not because it's a "traditional Irish instrument".

There are several very good concertina players around London playing Irish music on the English. There is a Comhaltas teacher in North London who plays the Duet! Personally I play Irish on the English - by accident rather than design - mostly with Irish musicians and no-one where I have played (including in Ireland) has ever suggested that I am playing the "wrong" sort of Concertina. I understand that Mary MacNamara, although renowned for the Anglo, also plays other types (English, Duet). If anything I find people generally know very little about concertinas and are interested in the differences.

You can probably play Irish music successfully on most instruments. I think it is down to the player not the instrument whether it is good or not.
Perhaps we should start a thread on "the most unlikely instrument I have heard Irish musiclayed well on". I could nominate the harpsichord for start.

Just get on and play. There are bigots everywhere (especially in certain forums on e-space where they are invisible).

Helen