Facebook's position was that if everyone started using this license, it would cut down on patent litigation. That might be true but I don't think it would be a good legal deterrent in practice. On the one hand, if you ask your legal department's permission to use React, they probably won't get on board with being bound to never sue Facebook; they don't care how great React is. On the other hand, if you use React without getting permission from Legal, and your company is thinking about suing Facebook over patent infringement and they find out about React, it might be a deterrent. But you can also bet some engineers are going to get fired.