[nocarrier]

I'm former FB Infra and agree with your first point re: motives. There's a lot of true believers working in the security space at Facebook, and I have tons of respect for them. I used to work closely with many of them.

However, scaling and/or capacity is not the reason E2E encryption isn't applied on all messages. The crypto operations are relatively trivial in terms of cpu.

This comment summarizes what FB's CSO said about why they are not launching E2E broadly yet. It boils down to usability concerns. Sounds like they are working on it:

https://news.ycombinator.com/item?id=12055567

[free2rhyme214]

Usability with Facebook M, much like Google Allo, will require E2E encryption to be turned off in order to take advantage of those features. Alex didn't mention that, but I think that's the real reason. Also FB wants to know what's going on in your conversations. That metadata can be used for advertising.