I don't understand Galahad. He goes around in a red robe to show off his purity, chasing after a cup that no one else can see. I find it very odd that he would want to live this way. He might consider himself to be knightly because of what he has--and hasn't--done, but it doesn't seem to me that he's actually lived. Arthur, and other knights, all fight and battle and do what they must and what they want, trying to stay within the bounds of knighthood, but at least they're actions make them men. Although, in their minds, I'm sure they only consider themselves sinners.
Galahad is strange. I wouldn't let him fight on my side if he begged me to.