Restricting public goods => artificial scarcity
Excellent question. I was not at Ouishare and have not heard Michel's talk, so I cannot say anything about it: but elsewhere I did hear a lot of talk about common goods. It seems to be in fashion. I think it's the name: hey, they are "common", so they must be sociable, friendly, they bring people together! They must be a good thing. So it does happen that people call "common goods" what are, in fact, public goods. Like Nadia, I would classify Wikipedia as a nearly pure public good,
Getting the name wrong means risking getting your policy implication wrong as well. Specifically: the whole policy problem around common goods is how to regulate access to them (this is the overarching theme of Ostrom's Governing the commons). Viceversa, for public good access regulation is no problem at all: what makes them public is the fact that their consumption is not rivalrous – if I consume an extra unit of a public good, this does not imply that someone else has to reduce their own consumption of the same good. Ostrom's examples are all very analog: forests (once I log one tree, no one else can log the same tree), fisheries (once I catch one fish, no one else can catch it again), aquifers (once I pumped a liter of water, it regenerates very slowly). The digital realm works by different rules: by reading a Wikipedia article, I don't take away anyone's possibility to do the same. If anything, the social value of a Wikipedia article grows with every perusal.
Consequence: you could try to monetize Wikipedia by putting it behind a paywall. Maybe it would be fairer towards WIkipedians. But it would definitely destroy wealth, because it would reduce the consumption of a good that does not deteriorate by consuming more of it. And since digital goods don't deteriorate with consumption, paywalling means creating an artifical scarcity – just as Hollywood does with the files of The Simpsons. The Pirate Bay's whole argument was that artificial scarcity ( which they view as a bad thing) is the opposite of sharing. If indeed it was suggested in a conference on the sharing economy – well, I'll be surprised, though I do sympathize with the fairness argument.
End of the comment. If you are not familiar with the economic argument above, read on for a silly example in the tradition of 18th century economists.
Picture an economy consisting of a single farmer that grows tomatoes. Tomato seeds are freely found in the environment, and they have price zero; so does fertile land. The economy contains an endless supply of Wikipedia articles with all possible information on the cultivation of tomatoes. The farmer divides his time between researching methods for growing more, better tomatoes and actually working the field. All the research consists on him looking up stuff on Wikipedia.
Now suppose a paywall is put around Wikipedia. The farmer has to pay (in tomatoes, for simplicity) every time he reads an article. At this point, he will be tempted to cut down on research activity: if he just grows tomatoes as he always has, he does not have to pay anything. If he is not curious or ambitious enough, he will then be content with doing just that. More realistically, he will adopt an intermediate solution, reading fewer articles than he would with the free Wikipedia (for example, only when a blight breaks out). Whatever the solution adopted, the point is this: the paywall forces the farmer and Mr. Wikipedia to share the tomatoes (so it might be fairer), but it also reduces the number of tomatoes to go around (it is less efficient). There is an efficiencly loss, as the farmer attempts to duplicate knowledge that already exists behind the paywall. The efficiency loss comes from the fact that knowledge duplication has zero cost: an economy that shares all knowledge is, all other things being equal, always more efficient than one that does not.
Economists have known for a long time that a system of market prices is great at allocating resources within the domain of private goods (rivalrous, excludable); and, conversely, that it sucks outside that domain. The price of a private good encodes information on its optimal allocation, whereas the amount charged for accessing a public good does not, and strictly speaking, is not even a price.