My overall thesis on fetishism, in general, is that a “fetish” is when a metaphor replaces the concept to which it refers. For example, the literary sense of being bound in chains is to have one’s free will reduced to practically nothing. So the literal meaning is that a person in chains cannot engage in moral actions which have real effects, and the metaphorical meaning is that a person can’t make any meaningful moral choices (fatalism). In a sexual context, this metaphor refers to the desire to be driven to infatuation by forces beyond one’s control (by fate, meeting one’s soulmate, etc.), and have no say in the matter. However, if this neural pathway is strengthened by association with sexual arousal (and particularly sexual release) and the original pathway is weakened by stress, disuse, or avoidance, then the metaphor can become the new sexual response pathway and it becomes a fetish proper (in this case, bondage fetishism).
The maladaptivity of fetishism (in general, not just in the sexual sense), and its tendency to spiral into extremes of perversion, is due to the divorce of form and function. Someone who takes Jesus’ admonition “Man shall not live by bread only, but by every word that proceedeth out of the mouth of God” to mean that he should consume the Bible literally may sate his appetite in the short term, by filling his stomach. But his stomach will complain all the louder in the long term because it can’t digest cellulose into nutrients his body can use. If the original hunger-satisfying behaviors have deteriorated, and the only neural pathway left is the fetishized, Bible-eating one, then he will double down and eat even more paper the next time. And this vicious cycle will continue until it runs into some sort of external limitation imposed by reality (in this case, death).
To take another example, consider spandex fetishism.
Tights, in the metaphorical sense, refer to idealism. This follows by analogy from clothing, which refers to symbolic pretensions. We immediately know a man is a king when we see his golden crown and magnificent robes, but if he is stripped of these representations we see he is a man as vulnerable as any other. A naked person is considered vulnerable because they can’t frame the appearance of their body to be something more desirable than it is, so in the metaphor a look at a person’s naked body is a look at their unadorned heart. And of course this would indicate vulnerability, because if people know the innermost convictions that drive our actions, they will exploit that inside knowledge to get what they want! A person’s only hope is to restrict this sort of access to people who want the best for them, i.e. loving, high-trust, high-investment relationships. This is why we developed the custom of hiding our “private” parts: it’s an assertion that our reproductive forms (functions) are sacred and don’t belong to any old schmoe in the public sphere.
Extending this understanding then, tights represent the form of nakedness without the function. A person in tights has the appearance of vulnerable transparency about what drives them, but in reality they are still presenting a simplified, coherent ideological belief system rather than the messy, complex, conflicted humanity underneath. Therefore, spandex itself is a metaphor for idealism in general (which is a fixation to begin with).