Wikipedia is forcing us to confront the paradox inherent in the idea of learners as "doers, not recipients." If learners are indeed doers and not recipients, from whom are they learning? From one another, it appears; same as it ever was.
How come Wikipedia hasn't turned into a giant glob of graffiti? It certainly would have by now, were it not for the multitude of volunteer sheriffs of the information highway who ride around patrolling the thing day and night.
There is a bogglingly complex and well-staffed system for dealing with errors and disputes on Wikipedia. There are special tools provided to volunteers for preventing vandalism, decreasing administrative workload and so on: rollbacker, autopatroller and the like. Then there are nearly two thousand administrators, who are empowered to protect, delete and restore pages, move pages over redirects, hide and delete page revisions, and block other editors.
The threat to Britannica from Wikipedia is not a matter of dueling methods of providing information. Wikipedia, if it works better than Britannica, threatens not only its authority as a source of information, but also the theory of knowledge on which Britannica is founded. On Wikipedia "the author" is distributed, and this fact is indigestible to current models of thinking. Wikipedia is forcing people to accept the stone-cold bummer that knowledge is produced and constructed by argument rather than by divine inspiration.