I had to check m-w's entry for "literally". While they do include a sense 2 that is similar to "figuratively", there is a substantial note afterwards and an FAQ

I had to check m-w's entry for "literally". While they do include a sense 2 that is similar to "figuratively", there is a substantial note afterwards and an FAQ that does a great job of explaining the status of the two senses and a touch of their history. They give some facts that contradict your above, as well (related to the timeline, as well as what constitutes slang). In case you're interested: https://www.merriam-webster.com/dictionary/literally https://www.merriam-webster.com/dictionary/literally I do think this is what the dictionary should say. It describes actual usage, including disagreements about it. By the way, I do think there is a place for linguistic prescriptions, it's just in style guides rather than dictionaries. E.g., fine for the Economist to decide "literally" will only be used in its literal sense in their pages.