Cindy Sheehan = anti-war screecher, protesting a legal decision that was ratified by Congressional authority.
Perkins = taking a stand in support of established law and opposing a change to the law. Further, the subject of his speech was not going to be on DADT as that was not the point of the gathering.
Not really seeing an equivalency between the two positions. Sheehan’s position was in opposition to good order and discipline so it would not have been appropriate to invite her to speak. Perkins’ position is in support of a law that ensures good order and discipline. His invite should not have been withdrawn as it shows the chaplains taking a political position on a matter that is under active discussion by civil leadership. That is not acceptable conduct by a military officer, even if wearing a chaplain’s insignia.
Both would have been people speaking out against stated government policy. Neither should have a place at an official government-sponsored event.