Regarding your second point -- that also includes the fact that you cannot sue any of the React contributors, not just Facebook. If I have a pull request on React, I can copy everything you ever built on React, down to the interface. It doesn't matter how much I copy because you cannot sue me without losing license to the very thing you used to build it, and thereby not having right to build it in the first place. Read the agreement in full, till point (iii).
> (iii) against any party relating to the Software.
No you do not lose the copyright license to use React in your code base. It is BSD. You only lose patent grants in the event you sue Facebook. In the event you sue Facebook, you're going to have to comb through your entire product code base and implementations for possible infringement against their portfolio of thousands of patents because you can bet your ass their legal team is going to come after you in retaliation. That is the nature of patent wars.
> (iii) against any party relating to the Software.