Austin, I don't agree with your general line of thinking. Everyone and their circumstances are unique, so what someone thinks are best practices for them may not be the best for you. You say that "If all that someone can say to justify their position is that 'it works for them,' it probably isn't a best practice." How do you know that? Like you say, you don't know what you don't know. I think the best we can hope for is to expose ourselves to different opinions and procedures, consider their merits, and incorporate part or all or none of them into our own view or ways of doing things. Finally, we sometimes do things in a way we know is not the best, whatever that is; we do them our way because that's the way we enjoy doing them.
Oddly specific circumstances aside, a "best practice" is objectively better than other practices. Example: driving with a seatbelt on is a 'best practice.' We can nitpick and find situations where wearing a seatbelt will cause more harm than good (such as wearing a seatbelt in a vehicle that is actively sinking), but it doesn't detract from stating that objectively, wearing a seatbelt is a better option than the alternative.
The same is true for firearms, self-defense, and other related topics. Most people are oblivious to the 'best practice' because they were either never exposed to it or are unwilling to challenge their thoughts and beliefs because something "works for them."
Some people enjoy driving around without a seatbelt because it is more comfortable. That's on them. My entire point is that going around and telling people that not wearing a seatbelt is better than the alternative because it "works for them" is a no go. Why? People come to places like this forum seeking advice and/or knowledge and we can all do our parts to help only spread the "better," more accurate knowledge.