If you work for a software company and your company has patents then keep in mind that by using React you are giving Facebook a free license to your entire patent portfolio.
More info on weak vs strong retaliation clauses: http://www.rosenlaw.com/lj9.htm
I believe a couple of lawyers have suggested that this could, maybe, arguably be true. However, no court has ever ruled as such, and the consensus among IP lawyers is that it's an unlikely outcome.
If you're worried about potential patent lawsuits, I would NOT suggest relying on the vague hope that someday a court might read an implicit patent grant into the BSD license, especially when you'll be facing off with Facebook's lawyers.
Or do you have some citation for the "implicit patent grant"? In particular, a court decision finding one?
My understanding (and I'm asking for correction, if I'm wrong) is that last year FB changed this provision to only cover patents on technologies within React itself, not "any sort of patent claim against Facebook", which WAS the situation before they changed it.
So, the current state is a grant of "you are licensed to use our React patents at no cost as long as you don't try to make a legal claim that any of our React patents are not legally ours."
The old grant terminated if, among other things, you argued that any Facebook patent was invalid or unenforcable. This meant that if Facebook sued you over an unrelated patent, you couldn't defend yourself without the React patent grant terminating.
The new grant specifically exempts any counterclaims; you can't lose your patent grant just because you defend yourself. You can still lose it if you sue Facebook over unrelated patents.
It's bad, but it's not quite that bad. Theoretically, you could stop using React, then start the patent litigation. Then Facebook could not sue you for React because at the time litigation started you were not using the license. But that's definitely a high barrier to jump if you've built up react as a core part of web and/or native applications.
The obvious next question is: what patents are necessarily infringed in the first place, just because you used React? It's a useful tool, but even if Facebook have successfully acquired relevant US software patents, it's hard to believe there's anything significant in there that had no prior art. GUI programmers have been specifying presentation details declaratively, using templates, and bundling updates for performance since long before the existence of React (or Facebook, for that matter).
Patents, and particularly submarine patents, have been a risk in the software industry for a long time. This is particularly true in jurisdictions like the US, where both the everyone-pays legal system and the recognition of software patents are unfavourable to the little guy in most circumstances. No doubt many of us don't particularly agree with or support the current legal position, but there it is.
So that brings us back to my earlier question, which I notice you haven't actually answered: for this to make any difference in law, Facebook would need to have relevant patents that will apply if you use React, so what are they?
And if your argument is still that it doesn't matter because they can just sue you and keep pumping money in until you lose through attrition in court, then this is all irrelevant anyway, because in that case surely there would be any number of other grounds they could use to support an artificial, aggressive lawsuit like that without even mentioning anything about patents. I don't really believe even the US legal system is that distorted, by the way, I'm just playing along with your earlier argument to show why it wouldn't matter even if you were right.