Ok, I see where you got that perception of my view. (I apologize for what, in retrospect, seems like a somewhat more confrontational tone than I intended.)
The thing about the comment "at most this is doing no good, and it's how I like to play" is that the part of it that makes a factual claim about the world outside the speaker's head... is, in fact, wrong. The approach in question may be how they like to play — fine and well — but it's doing worse than no good. That's the bias described in the OP: believing that something is worthless, when in fact it is worse than worthless (where "worth" means "contribution to effectiveness" or something similar, not taking into account enjoyment value, etc.).
So what the person is saying is "I prefer this play style, which is not any less effective than the one you advocate". If that were actually true, then I wouldn't have any issues with it. I also (in a different way) would not have any issues if the person instead said "I prefer this play style, which I acknowledge is less effective than the one you advocate". But as it is, the person labors under a misapprehension, and it affects their decisions; and insofar as we are interacting in the context of D&D (or whatever game), it also affects me.
I describe in this comment what exactly "the problem" is with being less than optimally effective. I'd be curious to hear your thoughts on that.
I think that we're actually envisioning two different scenarios, and I think that difference is behind a lot of arguments similar to this one. You are thinking (yes?) of an experienced player, who has found a play style he enjoys; is aware of the tradeoffs, but judges them to be acceptable or inapplicable to his play context; and who plays with people who accept (and even possibly share) his play style.
In that case, if someone comes up to you and says "Hey, you're doing it wrong! Your character could be doing better by selecting X, Y, and Z more powerful option!", your reaction, quite naturally, is to say "I know what I want out of this game and I'm getting it, please go away".
But that's not the situation I'm thinking of. Instead, I'm thinking of an inexperienced player (or someone who's less experienced/skilled than they think they are), who is not aware of the tradeoffs, possibly suffers from the sort of bias described in the OP, and, even more importantly, is playing with people in whose group the "alternative" (but actually just badly-thought-out) play style creates the sorts of problems I outline in my above-linked post.
My reaction to the former sort of player is to chat amiably about play style differences, and then not play with them. My reaction to the latter sort of player is to try to fix them.
My reaction to the latter sort of player is to try to fix them.
I am not at all sure that all inexperienced players need to be "fixed" by minmaxing them.
There are things that are worthless-- that provide no value. There are also things that are worse than worthless-- things that provide negative value. I have found that people sometimes confuse the latter for the former, which can carry potentially dire consequences.
One simple example of this is in fencing. I once fenced with an opponent who put a bit of an unnecessary twirl on his blade when recovering from each parry. After our bout, one of the spectators pointed out that there wasn't any point to the twirls and that my opponent would improve by simply not doing them anymore. My opponent claimed that, even if the twirls were unnecessary, at worst they were merely an aesthetic preference that was useless but not actually harmful.
However, the observer explained that any unnecessary movement is harmful in fencing, because it spends time and energy that could be put to better use-- even if that use is just recovering a split second faster! [1]
During our bout, I indeed scored at least one touch because my opponent's twirling recovery was slower than a less flashy standard movement. That touch could well be the difference between victory and defeat; in a real sword fight, it could be the difference between life and death.
This isn't, of course, to say that everything unnecessary is damaging. There are many things that we can simply be indifferent towards. If I am about to go and fence a bout, the color of the shirt that I wear under my jacket is of no concern to me-- but if I had spent significant time before the bout debating over what shirt to wear instead of training, it would become a damaging detail rather than a meaningless one.
In other words, the real damage is dealt when something is not only unnecessary, but consumes resources that could instead be used for productive tasks. We see this relatively easily when it comes to matters of money, but when it comes to wastes of time and effort, many fail to make the inductive leap.
[1] Miyamoto Musashi agrees: