What has holy water or communion bread crumbs got to do with queers? That analogy isn't the same. If gays were disqualified from being Christians, then you would have a point.
The point is someone coming to a rally, who doesn't share the views of those at that rally (one speaker in particular), and throwing something on him is completely inappropriate and wrong.
Were a Christian to do that (with communion bread, or anything else) to a homosexual activist, the left would be having a fit, screaming about "hate crimes" and the like.
Left-winged activists do that on a regular basis. Some gay activists threw gay propaganda leaflets in a Michigan church, during service, screaming "It's OK to be gay". This was in reaction to California's passing of Prop. 8.
Code Pink is notorious for pulling similar stunts, particularly at a Karl Rove book signing.
It's dumb and it's wrong. It makes for good YouTube fodder, especially when they try vandalizing stuff and get smacked down by the cops.