I know, for instance, that my mom would be seriously flipping out if Facebook were blacked out for her. If they asked her to make a call to get through, she would call immediately and yell at the people for making Facebook not work. This would happen millions upon millions of times over, which is why people want major sites like Facebook to participate.
I find it both scary and intriguing that a small handful of companies could have such a significant effect on the legislative process merely by presenting something in a negative light to their users, and requiring some action to affirm that viewpoint before allowing the user to access the service.
Taking Facebook down completely seems extremely counter-productive for everyone. Just a button that says "I called, let me through" should be good enough, there would be plenty of people who have an aversion to clicking through that without actually placing the call, and then Facebook (and its dependents, Zynga et al) doesn't lose 12-24 solid hours of ad revenue.
I strongly agree that if Google "blacks out" anything, they should restrict it to search only. Email and other essential services must remain accessible.
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