The argument is that somehow, photos of trains and platforms (not switching stations, conductor compartments, or control centres) will aid terrorists, and therefore that banning photos will make New Yorkers feel safer. So, basically, this is a stupid idea with an even stupider justification.
The Village Voice is holding a Forbidden Photos contest to shoot cool, arty pix of the NYC subway, and to kick it off, they've interviewed a bunch of photogs who shoot underground all the time about why they work on the subway:
I've found that most subway police officers think that photography is already illegal, and there's no way to convince them otherwise. So I've taken to carrying a copy of the law with me. The only people this [regulation] will affect is law-abiding citizens.Link (via Kottke)
An enormous amount of great photography has come out of the subway. Look at Bruce Davidson, who powerfully documented the run-down transit system of the '70s and '80s and its weary riders. He probably wouldn't have been able to get a permit at the time (no one knows if the MTA will even issue permits this time around!). Would we be better off without his art?