The goal of descriptivists is to collect information about how words are being used currently and to compile a dictionary based on that information, so what you

The goal of descriptivists is to collect information about how words are being used currently and to compile a dictionary based on that information, so what you said about viral memes is compatible with descriptivism. The best argument for prescriptivism has less to do with authority and more to do with people who have an interest in being able to communicate clearly. A better word than "prescriptivism" might be "subscriptivism". Presumably, we subscribe to the normal rules of the English language so that we mitigate miscommunication. Purpose matters. The person who demands that everyone use "octopuses" is just an elitist asshole. The science institution, which demands that its members conform to a precise standard of language, is just doing its job.