Facebook is not doing anything to further the internet reach. All they are doing is furthering the reach of their walled garden. There is little to no longterm benefit from this.
Beside the above obvious point, the real point is not whether there is a benefit to providing access to Wikipedia with strings attached. The real point is this: are we giving up more than we are getting if we consent to Facebook zero rating some content and putting up walls to deny access to everything else?
My personal option is that the bargain is very bad for all parties involved.