Fair points Bruce,
I agree that some faults that don’t strip fruit character can “contribute to complexity” as you say if it’s in balance with the wine. My point there is to draw attention to the double standard put forward by natural wine fans/drinkers/shows who for some reason have no problem with spoilage organisms but will draw the line at oak usage, whole bunch usage, sulfur usage, acid additions, etc… which also contribute to complexity when in balance with the other components of a wine, but in excess, also can obscure fruit/terroir characteristics.
What it has come down to, why that line is where it is, is because of an ingrained fear/distrust of manipulation in wine. Which I think is misinformed (and also not prevalent to this degree in other fermented foods and beverages for some reason). Winemaking by definition is intervention. Even choosing not to make a decision about a wine is still making a decision which will impact the wine in some way.
I can’t agree that the definition of wine faults are in any way arbitrary.
This might get into a whole other discussion about what is deemed desirable and undesirable in wine, which is subjective. But I have to ask the question here, how many winemakers are intentionally inoculating their wines with acetic acid bacteria? Or brett? Or VA?
VA in Italian Nebbiolo is a direct result of extended skin maceration, which is often necessary to soften the tannins. It is still a wine fault and that’s why there’s a legal limit to it.
Brett is a result of poor sanitation practices / not inoculating and mismanaging your sulfur regime.
If the shared goal of winemakers is to make delicious wines that to the most practical degree, reflect the place they are grown and show regional and varietal characters, then organisms which interrupt or subvert the conversion of glucose and fructose to ethanol and CO2 can absolutely be called faults, or at least charitably “happy accidents” to those who like the smell of fresh cow shit in their wines.
We have the tools and technology to understand more about the microbiological world than Pasteur could ever have dreamed of. I think it’s a bit rich in this day and age to neglect to do something to your wine and carry on as if it’s somehow more romantic or more reflective of place because it contains a spoilage organism.