Thanks a lot for your answer. The part about loopholes explains a lot. But I don't quite agree about the asymmetry.
If you use React, doesn't it basically mean that you de facto license all your patents to Facebook whereas Facebook licenses those required strictly for React? With Apache 2.0 or GPLv3, you would only de facto license patent covering the software and the author would de jure license theirs. With BSD, there is no de facto licensing from you, as termination doesn't relate to patent suits. If so, the new grant is okay for people who don't have patents but it seems unsuitable for those who do. Less patent suits overall would certainly be a good thing but this condition seems very one-sided.
"If you use React, doesn't it basically mean that you de facto license all your patents to Facebook whereas Facebook licenses those required strictly for React?"
No.
The only patent grants you give are through CLA's.
Otherwise, i'm not sure i follow the concern?
Say you use React and own patents. If you ever sue someone over patents, it may terminate your React license in the case where the defendant uses React. You may not even know it and keep using React happily after termination. Later, you can't sue Facebook without them countering that your use of React has been unlicensed since termination. Is this a valid concern?
While rereading the grant, I even wonder: (1) does the termination in the grant mean termination of the copyright license as well? (2) asserting any patent against "any party relating to the Software" could include end users since they receive the same license and grant.
If you use React, doesn't it basically mean that you de facto license all your patents to Facebook whereas Facebook licenses those required strictly for React? With Apache 2.0 or GPLv3, you would only de facto license patent covering the software and the author would de jure license theirs. With BSD, there is no de facto licensing from you, as termination doesn't relate to patent suits. If so, the new grant is okay for people who don't have patents but it seems unsuitable for those who do. Less patent suits overall would certainly be a good thing but this condition seems very one-sided.