Homophobia originates from within the historical quagmire of brutish sexual instincts, coupled with the vulnerability of desire.
Human beings have been around for a rather long time. Much of that time has been, by our standards, rather savage, brutal and uncivilized. We've been fucking one another all along and developing "societies" largely based around these fuckings. Or to put it more politely, society and civilization have sexual power dynamics built into them.
Fucking implies a power dynamic. In its crudest sense, the male owns the female(s) he fucks. He owns the children that originate from those fuckings. His female(s) and his children are his wealth and his legacy.
The male may have to fight other males to maintain his family herd. Males often fuck their rivals to prove their dominance. Today this is *mostly* done figuratively, through 'besting' them in some form or other -- thus all the forms of competition society has generated. But this has NOT always been the case. In fact, I think it could be argued that through much of early, more beastly human history, literally fucking your rival was fairly common. A 'real man' didn't just fuck his women, he fucked anyone or anything that attempted to fuck with him. To be male and to get fucked is to be dominated, shown your place in the hierarchy, shamed, made 'less than a man'. Etc.
In all the above there's been no mention of 'desire' (or any emotion, let alone intimacy). In this over simplification, sex is presented as male prerogative and dominance, to put forward the notion that *this* is how many (if not most) men relate to sex on a fundamental, primal level. We're all the progeny of the *survivors* of a brutal human history where it was often fuck or get fucked both literally and figuratively.
But, of course, desire can not be overlooked when talking about the power dynamics of sexuality because, from the point of view of the fucker, it represents a vulnerability, a weakness. A dominator can be led astray, even trapped or betrayed by his desires.
This is how the power dynamics of a heterosexual relationship 'even out' (so to speak). It explains why women wish to be and remain 'desirable' because it gives them *power* to 'attract' and 'keep' the attention of their male counter part (and the social standing that goes with it). A dominator male must be careful, therefore, to not succumb totally to his desires, least he become 'pussy whipped', so trapped that he ends up getting 'fucked'.
It is from this historical quagmire of sexual power dynamics that homophobia has emerged. Ultimately it is FEAR OF DESIRE, that is, fear of weakness, fear of loss of control, fear of loosing 'dominance' and 'manliness' and, thus, fear of getting fucked!
In its externalized form, it is reassurance that one *MAY* fuck another man (figuratively and literally) as a form of dominance, free from any desire other than that of domination itself. But one must never DESIRE the opposite, to get fucked. Any male who does so is represented as weakness, and scorned as a direct threat to the social (hierarchical/dominance) order.
Internally the secret desire to give pleasure to another male or get fucked is an upheaval in the socially instilled hierarchy of the mind. It is a direct threat to the male dominator principal itself. One fears it precisely because it is seen as representing weakness leading to subjugation and possibly banishment.
I'll end this by suggesting that PERVERSION IS THE USE OF SEX AS A WEAPON. From this POV, if what I've said has any credence, the whole of our hierarchical / male-dominance civilization IS BASED ON SEXUAL PERVERSION.
Thus homosexuality is, in fact, a direct threat to the established social order precisely because it is a *potential* rectification of this perversion. Acceptance of the subjective experience and external expression of *mutual sexual desire* irrespective of gender is a huge step away from the hierarchical, male dominator culture that has been human history for tens of thousands of years.