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.