It's too bad, because the best managers I've worked with were not good ICs, but they did multiply the effectiveness of the ICs they worked with, and so were absolutely invaluable to the company in a way that may not have shown up on paper. If those people exist in FB, as I'm sure they must, then they'd presumably get jettisoned as a result of this choice. That would be bad long term. I used to despise managers, until…
I've worked in a few environments where managers were replaced. Only then can you really make the distinction between great managers and bad ones. With one you think "wow this is such a tough business, the manager is doing crazy effort to keep things going", and then another manager jumps in and "wow, this is an easy project. Manager is taking a walk through the park. All seems like a piece of cake."