Earlier quoted context omitted.
Some of RMS opinions are extreme, because they take to an unbearable point some consequence of some ideology. For example refusing to have kids is extreme, most people cannot afford psychologically to not have kids. But RMS opinions about Facebook are not extreme, he doesn't propose to refuse to have friends who are using Facebook, for example. He says just don't use it, it's common sense, just like don't eat fast fo…
"Don't use Facebook" is currently not common sense. Many people are on Facebook and have thought about all these arguments and decided it is worth it to them. (In the meantime, fewer people seem to consider it common sense to be on Facebook, at least it seems to me less and less people are surprised if someone doesn't use it)
Another example is abolition of death penalty in France by Mitterand: right now we French/Europeans believe it is very barbarian to still have Justice use this gothic expedient, and rightly so if you ask me. But just before its abolition polls showed most people opposed the abolition. A new, better "common sense" replaced an old habit falsy believed to follow "common sense".
So back to Facebook: right now most people do not know it, but it is not unlikely that the retrospective "common sense" of the future will be to avoid Facebook today. And I think a much saner regulation on what can be advertised and sold as food to human being in the US will also be retrospective common sense. And not driving cars is also common sense. The list is quite long...
[edited typos and grammar]