This is just patent-suit MAD ("If you sue, or counter-sue, us for patent-y stuff, your license to use the patents underlying React is forfeit."), not "You can't

This is just patent-suit MAD ("If you sue, or counter-sue, us for patent-y stuff, your license to use the patents underlying React is forfeit."), not "You can't use React to do Facebook-y things." There is absolutely nothing in the grant of patent rights that supports the second notion.