Web site blocking is oppressive and won't work
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Whether it's copyright trolls wanting to censor filesharing web sites to extract high prices for their content or the UK Prime Minister wanting to shut down social networks during times of unrest, web site blocking is oppressive by its very nature. In addition, it won't be effective.
Worse still, attempting to block web sites gets you some pretty dodgy friends. At the same event, it was mentioned that the Government's plans to block social media during times of popular unrest had drawn applause from certain countries that you "wouldn't want to get into bed with".
So the government is going to block web sites? It can try, but it will be fighting a losing battle. Censorship of the internet is oppressively draconian and simply will not work, so even to attempt it is pointless.