Arguably, one can't truly say the GC is optional, unless the language and its libraries were truly designed to work without it. In languages like Vlang, that's the case, as the GC was a late addition. If turning the GC off cripples the functionality and usefulness of the language, then there is little point in using the option.

Probably a better argument for Go (and other languages like Java) is how "tweakable" the GC is or at least describe it as the GC can be turned off, but it's not designed or useful to do so.