I don't think Facebook's business would be at risk at all if they open sourced most of the backend code. As long they kept things like spam/malware detections c

I don't think Facebook's business would be at risk at all if they open sourced most of the backend code. As long they kept things like spam/malware detections closed. Facebook's main value proposition is the existing network. Another network could possibly overtake them some day, but they're definitely not going to be doing it with Facebook's source; not even a heavy fork of that source.