As I wrote in the other forum, my feelings agree with cessna here. It seems like this would be much more dangerous if the controllers timed the release for departure wrong or if an aircraft didn't follow instructions properly to keep separations.
Using a different airport as an example: Parallel runway operations at LAX. Let's deal with the 24's. When traffic is on final for 24R, they usually position and hold an aircraft on 24L. This aircraft is released when the traffic is on short final. I understand that this greatly prevents any LAHSO dangers. There are times, however, when the outgoing traffic is cleared for takeoff pretty early so that is a go around did occur, takeoff would have to be aborted. The controllers probably time it right so safety isnt compromised, but if ABC7 news was eating lunch at In N Out and watched this happen, I'd put money on an article about a dangerous procedure called aborted takeoff.
Back to JFK. Now, ATC will have to figure out what to do with the SAME number of planes as before, but without the ability to pack them for landing or takeoff as tightly. It seems like more delays getting into the air = taxi times, fuel costs, bored pilots, pissed passengers, etc....