I’ve been waiting 15 years for Facebook to die. I’m more hopeful than ever.

But high switching costs have their limits. If you make your service terrible enough, a certain number of users will find the cost of switching preferable to the pain of staying. And as users leave, network effects start to work in reverse: though every user that joins makes your service more valuable, every user that leaves makes the service less valuable. If you’re only on Facebook to stay in touch with a small group of friends, each one of those friends who departs makes it easier for you to make the jump, too. And once you go, it’s even easier for the rest of the group to bail.

This is very bad news for Facebook. After years of slowing US growth, Facebook just experienced its first-ever US shrinkage, which precipitated a $230bn stock crash, the largest in global corporate history.

Though most of Facebook’s users are global, its US users generate far more profit than users in the rest of the world. Losing a US user is expensive. Even more important: the US is Facebook’s home base, and its US user base is its main bargaining chip in resisting US regulation, and in securing US support in its regulatory battles abroad.