Just because you can, doesn't mean you should.
The reason I chose not to fly was not because of the "No Drone Zone" sign, but because this was a wildlife refuge. The area was teeming with birdlife and flying a drone in this location would surely be disruptive to their habitat in all kinds of ways.
I think national parks should be off limits for drones, as the arks are there as a way to preserve nature for everyone to enjoy. Nothing kills the moment like a machine buzzing overhead.
As pilots, we need to be respectful of other people and the environment. If we don't act responsibly, we are going to see tighter and tighter restrictions until there's no place left to fly.
I love to fly and I am sure I have flown in a few places where I shouldn't have, but I am trying to be more responsible in my decisions as a drone pilot.
I'll get offa my soapbox now....