The internet, and content sharing platforms like Youtube, have engendered a new era of access to multimedia expression, and it would be really sad if the big boys were allowed to throw their weight around too much in those places.
You have to realize that Youtube itself is one of the big boys.
It's good to actually see fair use actually get some legal backing. But the comments that Content ID is good enough to check the fair use or not box is worrying. For such a nebulous concept like fair use you really need human eyeballs on a case by case basis.
I disagree. A well defined metric would help fair use in a big way. If left to interpretation, the side with the best lawyers will always be able to make a better case. Not to get political or anything, but look for instance at the 'war on terror'. It's impossible to define the enemy and the win conditions, and therefore it's become this umbrella justification for pretty much everything 'they' want.
Clear definitions, even to the point where a computer algorithm can do the checks, are almost always preferable over these nebulous concepts. If something means too many things it'll stop meaning anything... or it'll mean whatever they want it to mean.