It hardly matters now, but as gets pointed out every time this gets brought up, this is quite false.
You would lose the legal right to use any patents which Facebook might (or might not!) have on React. You did not lose the seperate BSD license on the actual code with grants you your license to "use react".
> Using React no longer increased your vulnerability with respect to IP or lawsuits pertaining to Facebook.
That's highly debatable. If Facebook does have patents on React (and it is believed they do), then using React, or any technology that uses the same underlying technology does, in fact, increase your vulnerability to IP disputes and lawsuits from Facebook. :) The implicit patent grant in the MIT/BSD license will help, but so did the (now removed) explicit patent grant, so it's hardly clear this is a win on net.
The situation has never been as simple as people seem to wish it was. Software patents are an enormous and (so far) unsolved burden on our industry. At least if you're in countries where they are enforcable (and given the nature of the global legal system, probably even if you aren't).