Im not so sure about that, given their virtual monopoly. I also think that changes when you have more users than some nation states have population. It can be quite damaging for some to be barred from using a service like FB and Twitter, given that many other services use these sites to spread possibly vital information. Off the top of my head, how much information from politicians would be missed out on if banned? Could this hurt the democratic process? With out realistic competition this will in time get worse. What if reasonable protest is some how seen as unpatriotic?

I cant help thinking that as some point there needs to be an independent arbitration service that users or ex-users can appeal to in this sort of event, perhaps one a site's user base gets to a certain level. Other wise, how are facebook and co ever held to account in this respect? Can a Syrian protester sue facebook in Syria, or perhaps raise a fortune to sue in the US? How does it work?