Well that is a good question, since that one that was chained up WAS damaged, it was still able to move - but it was in pain. So yeah, what WOULD stop someone from simply going "okay those are Weeping Angels", grabbing some C4 while SOMEONE looks at it, YOU can blink or close your eyes, but SOMEONE has to be watching it. So why not just load it up with C4 or even just whack that sucker with a sledge hammer, jack hammer, whatever and turn it into bits. Granted a Statue of Liberty IS going to be hard - but that's one thing that took me out of the episode - you THINK if the frickin' Statue of Liberty was able to somehow "reeeally fast" move all the way from Liberty Island into the heart of Manhatten - NO ONE WOULD BE WATCHING? I mean c'mon.