I can't help but think in people who refuse to get formal training (in the context of "tactical firearm use") are acting to some degree out of cognitive dissonance.
If you do it "your way" for years and practice a lot, it might kind of hurt to admit that there could be a better way. Thus I think people avoid formal training even when it may be beneficial, so as to avoid admitting - or finding out - that "their" way is wrong or suboptimal.
Sure, some people can't afford it, but let's be honest: most people on this forum have 3-4 handguns costing $300-1000. That's probably below the median actually. I can't help but figure that aside from the people who are genuinely unmotivated to train (which excludes our hypothetical "self-taught" frequent practicer, anyway) or unaware of the benefits of formal training (which excludes most anyone on the internet, or who can engage in even a superficial amount of thought as to why many police, military members, etc, go through extensive training rather than wing it), most of the people who avoid training are avoiding it because they're afraid they'll be shown they don't quite have it nailed.
If someone was self-taught and could afford a class, and had an open mind, I'd be surprised if he came up with a
good reason to avoid formal firearms training altogether. If you're self-taught, you can surely admit there's some limit to what can be achieved solo...I have trouble believing people who are self-taught truly think they are using 100% optimal methods, etc. Self-teaching works to a point but there is a reason we have schools/education to teach people things, employers training employees, and technical and skilled labor is in high demand: people simply don't self-teach that well most of the time.
I think I made my point but if anyone doubts it, have a look at a few of the comments posted earlier. If your best argument for avoiding formal training is "Those guys are a bunch of blowhards/idiots"...maybe you ought to consider that you're acting out of cognitive dissonance.