Meanwhile there's no sign that any tech giant will ever be more than a short blip in our history. Not sure why we should sacrifice our privacy so a shameless parasite lives a few years longer.
Foreign companies are:
1) Taking away valuable citizens data
2) Taking away ad money
3) Not paying taxes
If anything it's an economic suicide to support the status quo.
Facebook leaving is a huge threat. I think you are underestimating how big a role it (or its other services) play in people's lives. If FB/Messanger/Instagram/Whatsapp disappear today in some European countries and the government's explanation was "we didn't manage to make an deal" I don't think that government would last for much longer.
It is also correct. Every European company using FB/IG are acting illegally. It is only illegal if you get caught. So, just like speeding or overloading your truck using FB gives you an advantage until you are caught.
The world would be fine without Facebook, other people will step in to fill the void.
No one wants to live in a museum.