Do usage errors exist?

Solution 1:

A language error is the use of an expression which does not conform to the system of that language. To the extent that people have different ideas about what the language system of English really is (which extent is considerable), they will disagree about what things are errors in English. "Error" is a theoretical idea -- you have to have a theory to recognize deviations from that theory.

Solution 2:

Linguistic descriptivism is not about what is good or bad usage. It's a social scientific field that wishes to describe how people use language. Now, does that mean that the linguistic descriptivist thinks all usage is appropriate in all contexts? Of course not.

Good usage is intelligible, not confusing, and accurate. In different contexts that is going to mean different things.

If you use the philosophical-legal usage of 'begs the question' to most American English speakers, you will not be understood by the listener. In which case, it would be a poor choice of language.