If initiating a patent war with Facebook is a foreseeable business outcome for you, then you probably shouldn't use React. I remain convinced that logic applies to only a tiny minority of companies.
My reading of the license is that you lose Facebook patent grant even if your lawsuit was a response to Facebook's.
I am not a fan of (software) patents, but license restrictions are not limited to them either. So what is your recourse if Facebook decides to infringe yours?
Assuming this is true (IANAL), would you still feel as comfortable advising companies to use React?
I don't begrudge Facebook for their license for the same reasons that Matt stated, but I am highlighting this issue to my clients and would not recommend React's use because of it.
"Does termination of the additional patent grant in the Facebook BSD+Patents license cause the copyright license to also terminate?"
"No."
This might be the one[0].
"Additional Grant of Patent Rights Version 2 ... The license granted hereunder will terminate, automatically and without notice, if you (or any of your subsidiaries, corporate affiliates or agents) initiate directly or indirectly, or take a direct financial interest in, any Patent Assertion"
Seems clear to me that you lose the license to use React. The clause that terminates the license is contained in a grant of rights, but the license it refers to, is the license to which this grant of rights is an "addition".
Moreover:
"A "Patent Assertion" is any lawsuit or other action alleging direct, indirect, or contributory infringement or inducement to infringe any patent, including a cross-claim or counterclaim."
The "other action" is pretty broad and might as well include "use your patents in any way that goes against the interests of Facebook".
Reading legal documents with a benevolent attitude towards the claims, intentions and goals of the issuer is a pretty bad idea. If anyone decides they won't ever have or deal with patents and thus they are free of danger, that risk is up to them; but don't do it because you think the clauses only cover a narrow and unlikely set of situations.