Sure there's a lot of value in communicating with other Facebook users, but if you can't see the possible downside of having a large group of people's first and only connection being through a corporate-controlled view of the world, you're not using your imagination.
So not only does it prevent competitor websites, but it stops competitive ISPs, too. It's especially bad if this coporate network is censoring information. No opportunity to even discover non-filtered information outside the info bubble. This triple whammy is the consequence for those involved or not.
This is only an intentional effort to control and shut out competition (e.g. future Facebook competitors) and has the risk of killing local ISPs as a by-product.
tl;dr It only serves Facebook. Wikipedia et al. are just thrown into the mix to make it look like a humanitarian effort.
How on earth are we going to get them innovative/affordable internet solutions if no one can compete to get there?
1. http://freakonomics.com/2011/02/15/what-happens-to-all-those...