Your example is solely if THEY initiate a lawsuit then you're allowed to respond, not if they do something against you that warrants suing them first. Note tha

Your example is solely if THEY initiate a lawsuit then you're allowed to respond, not if they do something against you that warrants suing them first. Note that this is specifically regarding a patent assertion; i.e. the patent grant is not revoked if you bring legal action against Facebook for another reason, including trademark or copyright issues. Edit: E.g. They can copy your whole business, design and all, and if you're using React and sue them - then they can use that against you See above – this would specifically only apply to patents. you'd have to immediately cease using it This is not necessarily true – it just means that you lose your patent grant to React. There is no assertion here that Facebook hold any patents on React. It's obvious why this would be the case – if you bring a patent suit against Facebook, then they revoke any patent license they've granted you. I would expect any patent license – for open-source software or otherwise – to be the same. Granted, this does nothing to affect the wider issue of a broken patent system.