I agree that it is frustrating to have to constantly push back against the hysteria around the license, however, I think parent was correct in their initial assertion - "The problem is if you ever found facebook infringing on one of your patents, you could not sue them -- your react patent grant would be rescinded.".
While rescinding the patent grant does not remove your license to use the product, I've seen some lawyers argue that Facebook's license is weaker than a "regular BSD license". The argument goes that a "regular BSD license" has an implicit patent grant that is stronger than what the React license offers through its explicit patent grant. Thus, you are not reverting to a "regular BSD license", you are reverting to a "regular BSD license MINUS the implicit patent grant".
While rescinding the patent grant does not remove your license to use the product, I've seen some lawyers argue that Facebook's license is weaker than a "regular BSD license". The argument goes that a "regular BSD license" has an implicit patent grant that is stronger than what the React license offers through its explicit patent grant. Thus, you are not reverting to a "regular BSD license", you are reverting to a "regular BSD license MINUS the implicit patent grant".
(http://en.swpat.org/wiki/Implicit_patent_licence#USA)
(IANAL so I have no particular understanding whether this is a good legal argument, but assuming it is, it seems like a strong counterpoint).