As a former POW, McCain is a moral free agent. If he chooses to embrace Kerry despite the egregious harm Kerry loosed on him as a POW, that's his choice.
However, McCain has no right to demand that other POWs join with him in embracing Kerry. He has no right to condemn other POWs for honestly and even emotionally calling Kerry to task, especially in view of the fact that Kerry has made his Vietnam experiences the focal point of his campaign.
Yes, it's his choice and no he doesn't have the right to expect other POWs to join with him. However, if he calls this "dishonorable and dishonest" or any phrase meaning the same thing, it will come back to bit him in his own home state, IMO.