I think perhaps you both are missing the point, or missing some information, regarding the Boston parade. The parade, a private one, is organized and run by the South Boston Allied War Veterans Council, which is in turn run by a bunch of old white conservative guys. The gay group that wanted to march was the LGBT Veterans for Equality, an affiliate of Mass Equality (the folks who helped bring us same-sex marriage). Another group that has also been refused entry into the parade is Veterans for Peace.
So the organizers, all veterans, sponsoring a parade for Irish veterans, is actually rejecting more than just LGBT veterans, but those veterans who differ politically from them as well. It’s a bunch of reactionaries who are using the status as a private organization to push their own political agendas, one of which is gays suck (ok, pun intended) and another is that war is glorious.
It may be run by a private organization, but with taxpayer money being used for security and cleanup, and with millions predicted to attend, this is really a public event, and thus exclusion of ANY veteran’s organization should be anathema–and it is to some corporations, many politicians, and tens of thousands of the public.
I hope you can see that this is different situation from those other parades you mention, Kieran.