One thing I don't get is why did it have to be acquisition. If FB had just acquired 10-30% of the company at 2G$ valuation and left control to the other people

One thing I don't get is why did it have to be acquisition. If FB had just acquired 10-30% of the company at 2G$ valuation and left control to the other people they would have had once again first class access to the technology but the backlash would have been smaller. Acquiring stake validates the technology. Buy outs - they mean you try to lock the other away from it.