Basically, this whole diversion should demonstrate two things to you.
First, that you shouldn't play the game of semantic uncharitability without being absolutely semantically beyond criticism. If you insist on being a pedant, fine, but be authentic in your pedantry, rather than just using it as a tool to poke cheap jabs at other people in a debate.
Secondly, that even in accepting the idea that there is a matter of fact about semantic interpretation, you are committing yourself to certain oughts and shoulds. At this point you might trot out Hume's "is-ought distinction", and in response I will point to the idea of semantic protocol (in, say, Gricean semantics) as constituted by conventions and psychological properties of human beings.
If you're going to go play the ethical nihilist, do not try to correct peoples' use of language.