I think the "rude photographer issue," as bowlofpetunias referred to this oft-raised topic, can be attributed to a number of things: lack of situational awareness (or "obliviousness" as Saboteur said), lack of control in the water, a sense of entitlement to get the shot, a sense of having only a limited opportunity, competitiveness with other photographers, and perhaps more. In any given instance, a photographer may succumb to at least one of these. There is more to underwater photography than just taking a good picture, and even more when you're among other divers. I haven't taken an underwater photography course, but I would hope this is not glossed over.