AS a minister, a photographer, and a trained chaplain to first reposnders, I can tell you, first of all, that if you have not been "detailed" to a particular scene, then it has become increaingly difficult, since 9/11 credential or no, to get beyond the outer perimeter.
In many cases, even the best intentioned individuals are turned away because of concern that they will just get in the way of those whose job it is to respond constructively, emphatically, and expeditiously to catastrophe. That was the experience of many at Ground Zero. As time went on, even on day 0+1, it wsa very hard and incredibly time consuming to get "cleared" to where the news (and the photogs) were happening, and for good reason.
Now, I'm talking about situations that are much more dire than those which most of the prior posts contemplate. But I want to suggest that in some situations a bogus credential could actually get one in more trouble than one might wish. Those in command at even the most routine, if that's the right word, automobile accident scene, for instance, would be abruptly put off by civilians walking around with weak credentials wishing to take pictures.
For my part, as a chaplain, I would not be well disposed towards those who would bend the misfortunes of others to their own ends, and it's hard to see how picture taking passes that test. Yes, there might be secondary or tertiary benefits down the raod, as it were, to great street photograhy in these instances, but the days are mostly gone when a potographer can pull a Weegee and get pics of the vics before the cops arrive. Give it up.
A lot of people "in command" think that the whole country is inside the perimeter since 9/11 and they react accordingly. They, in the word of an old song,, "are more to be pitied than censored." Though I think compassion is more in order than pity. These folks, and maybe some of you, have bought into the fearmongering fomented by the powers and principalities of the present age. Part of our work, IMHO, as image makers is to stand against those dark influences.