I think it would be extremely electorally damaging to ban such a major site, because it would affect so many people, even if people aren't hugely openly fond of

I think it would be extremely electorally damaging to ban such a major site, because it would affect so many people, even if people aren't hugely openly fond of Facebook, there would be a huge amount of outrage and anger that the government has cut people off, even if it was for the right reasons.