You do have to view the claims with some skepticism considering those making the claims stand to benefit substantially from people believing them, true or not.
The source of the negative sentiment may boil down to the cold calling. It seems to be one of those things that just hits a nerve, and I wouldn't be surprised if you could trace the anti-Yelp movement to this business practice. The other thing people complain about a lot is that their reviews aren't counted (presumably because of the anti-spam filter). If Yelp fixes those two major problems, it will be in much better shape.
you want a business with poor consumer reviews to be able to delist itself? Isn't that like being able to delete your case record with the Better Business Bureau?