I think this sort of question is being argued with youtube-dl and we can see where it goes. The entertainment industry argues the purpose of youtube-dl is to pirate content. Youtube-dl argues that there are in fact many legitimate uses for it and this argument has so far prevailed.

In the case of WhatsApp, the app has many legitimate uses, notably speech, which is often protected as a right. In the case of Tornado Cash, the app's only use is concealing the origin of financial transactions, which some could argue is never a legitimate use (and which others would argue is a legitimate use). Maybe the final arguments will come down to this legitimacy.

ianal etc.