The spirit of the actual license appears to be toward specifically preventing patent litigation against Facebook _and contributors and related entities to React

The spirit of the actual license appears to be toward specifically preventing patent litigation against Facebook _and contributors and related entities to React itself_. Assigning it to "competing with Facebook" in general seems a little broad. IANAL, but this could be seen as a needed protection and Facebook playing it safe in the interest of both itself and its open source contributors, kind of saying "if you contribute to, use, or are involved in React, everyone has to play nice and mutually agree not to sue each other over software patents. If you do, you don't get to benefit." Then again, you could take it the other way, and assume it could be used on the offensive. But I think there would be enough pressures against that type of use. Still, sure, consult a lawyer. Edit: the last part seems to grant some pretty wide freedoms, protecting your right to use React even if Facebook sues you over a patent unrelated to React, so with that in there, I think it's making it abundantly clear that this clause is about protecting React from patent litigation. Seems solid.