Prescriptions and descriptions are not opposites. They're orthogonal to each other:

• when you tell people how things are, you're being descriptive;
• when you tell people how things should be, or what they should do, you're being prescriptive.

And prescribing is not automatically wrong. For example if I were to tell someone "don't call us Latin Americans «spic niggers», it's offensive", I am prescribing against the usage of the expression "spic nigger"; it is prescriptivism. Just like when someone proposes inclusive language.

What is wrong is that sort of poorly grounded prescription that usually boils down to "don't you dare to use language in a different way than I do, or that people did in the past". It's as much of a prescription as the above, but instead of including people it's excluding them.

Tagging @[email protected], as this addresses some things that they said.