Whose law? The internet is worldwide.
You might have noticed that here it is about US persons (citizens, or residents), on US soil, dealing with US companies, on US soil. The traffic never leaves US soil.
Being on the Internet does not magically make you a Sealand citizen where you would not have to comply with any laws from any country.
Sure Facebook could apply the same tax evasion tricks to avoid to comply with governments laws, but then they would have to move all their employees to some tiny island nation, as well as all their servers.
Good luck with that. As far as I can tell, the majority high level talent loves to stay in the Silicon Valley and Facebook would end up with only crappy employees, or employees that they would have to pay a lot more. Not really viable.
The other option to store all the servers outside of the US (for US traffic) would mean that the site would be painfully slow, and then users would actually move to, and stay, at an other social site like Google+.
Now imagine that Facebook actually did all that, well how to they make revenue on these US users ? By selling ads, and the money would come from the US. It would not be too difficult for the government to lock down the money flow. Well maybe not the current US politicians, but not above the european governments which still (mostly) value people before corporations.