There are usages about which speakers widely disagree. Fluent speakers substantially agree on how these resources are effectively utilized. The flip argument has also been often heard. It is that usage will change an artificial language once it is launched, indeed change it beyond recognition. It will lose the advantage of its initial simplicity and logic and will break into competing dialects.
Simplicity wins, it turns out.
The pressure of usage by a large and diverse community of speakers does indeed generate ever evolving conventions of usage. This has happened to Esperanto, too, as its inventor Zamenhof forecast. But as with all living languages the actual grammar was too complex to codify fully. One reason may be that concern with simplicity and logic saturates most of the self-conscious linguistic intuitions, judgments, and innovations that occur. But, unlike natural languages, influential speakers and writers in Esperanto are not confined to a single country or language community.