Hi Mick,
'Stage Irish' doesn't necessarily mean it was performed on stage, although many of them were, with the singer (who had probably never been to Ireland) dressed in appropriate exaggerated costume with exaggerated Oirish accent. In the early 19th century they were extremely common and 'stage Irish;' simply refers to a type, as numerous examples appeared on broadsides. They rank alongside minstrel songs and country bumpkin types among others, satirising certain groups of people. They were all popular in earlier periods but the early nineteenth century seems to be the peak period.

I take your point that nowadays, quite rightly, it is more considered an anti-war song, but that's not how it started out.