> The same can be said about (good) unlicensed doctors, people who start computer programing/web designing/working with media editing apps as a hobby, and a lot of car mechanics, just to name what comes to mind.

Sure, if you pick your areas of expertise, you can find examples where self-study will teach you a lot. However, I would most definitely not include doctor in that. "Singer" isn't even an intellectual field of study, and neither is "car mechanic".

And you're basically saying that if you put in an equivalent amount of effort by yourself in certain fields, you can be as good as licensed expert in that field. This is certainly true for many fields, but has pretty much no bearing on the discussion at hand, because most people who edit Wikipedia haven't put in that kind of effort.