The patent grant isn't the problem it's the termination on any action against Facebook. Hence if Facebook infringes on patents you own you can't take action against them if you are using React.
1. filing a patent infringement against Facebook (for anything, related or unrelated to React)
2. filing a patent infringement counterclaim against Facebook for patents related to React (after Facebook have first filed a patent infringement claim against you for patents on anything)
3. filing a patent infringement against anyone for patents related to React
[edit]
> if Facebook infringes on patents you own you can't take action against them if you are using React.
You can take action against them, you just don't have a patent grant once you do.
Which opens you up to being countered-sued right? It seems that this leaves Facebook to freely infringe on any patents of React users without consequence.
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Also, patent lawsuits are costly. If you're going to start one against Facebook the cost of switching away from React first would be negligible.
Umm, no. You can still sue them, but the patent grant is nullified, which takes you back to the place where no such patent grant exists.
Hence, you're strictly better off with the grant.