Except you are about to define the terms under which it is indeed irrational, below.
...and eating doughnuts and chocolate ice cream turns out to be irrational.
Uhm, yes, that's what I wrote.
It will of course depend on the individual's set of desires and circumstances. IF eating a donut would be a serious health threat given someone's poor health, then it would not be the rational choice given the much stronger concern.
But IF someone is in good health and a donut isn't really going to impact that (and or they are not addicted to such food), then it's perfectly rational to get pleasure out of eating the donut.
So let's apply this to audiophile choices. Is there an overarching set of desires? Well, yes: experiencing excellence in sound reproduction.
Caveats: In the terms relevant to the individual audiophile. Your pinnacle of sound reproduction may not be what another audiophile is looking for.
If one doesn't have that as an overarching objective, I think I can argue that one has just disqualified oneself from the category of 'audiophile'.
Being an audiophile is typically not just about the gear, but about a passion for listening to music. For most audiophiles the two go together, in that they are looking for a compelling music listening experience from their sound system. Most of us want high quality sound, but in the service of increasing our listening pleasure. Therefore there will be individual variations as to what type of presentation combines both the more compelling sound quality AND the more compelling musical experience.
It then becomes irrational for the audiophile to make choices that diminish his or her experience of excellence.
The audiophile often balances his particular taste in sound quality and selection of gear, and playback medium, to ultimately serve the goal of the most compelling listening experience. People are different, so this choices will be different. (So strange to have to repeat this for over 300 pages every time another attempt to denigrate the choice of records comes up...)
Nobody has to have The Best Most Accurate Possible System In The World in order to care about and enjoy good sound quality.
In my case I care very much about high quality sound, I note that vinyl can often offer high quality sound, by my lights, so that audiophile aspect is satisfied. Plus I have playback gear far more elaborate and higher quality than the average music lover, because I am interested in audio gear. Further I love the gear associated with vinyl - turntables. So that's another audiophile aspect. And the other ways playing records influence my enjoyment of the experience, for me, easily override the often minor sonic quality differences I hear between my digital and vinyl sources.
So my choice for playing vinyl is extremely rational. It fulfills my specific desires, and seems to me a net positive in my life rather than a negative.
Note that this doesn't sit well with the notion of "just enjoying myself the most". If one is enjoying oneself the most with non-excellent sound reproduction.... well, that's exactly what non-audiophiles do, too, so one has become a non-audiophile.
cheers
Nuance, Newman. Nuance.