>> "it is insanely convenient and easy to lock-in users and restrict freedoms."
I agree, but is that really a bad thing? We all have to make money somehow. I'd rather website owners had real incentive to please their users, and being able to make money is a good incentive.
I don't see how open source can really be relevant on the web. If facebook want to do something to drive users away, or ristrict users freedom, that's up to them. If they do it enough, someone else will setup a rival website that pleases users better. How does open sourcing fit into this? I don't think it does. Most website is simple enough that you don't need free source code. Any one of us could clone facebook if we had enough time and determination.
Open sourcing is certainly a nice thing to do, and I'm sure we'd be lost without our own favorite open source tools, but I think it makes less sense on the web.
As I've said before, I don't use X because it's open source, I use it because it's free, and there are people behind it who care.
I think that's all that matters really.