But precisely what about the fictional genitalia in question is "callow, juvenile and immature"? That anatomical detail is described as looking "petalled", and that's where its resemblance to actual flowers ends, despite the jokes which stretch the metaphor too far.
Firstly,
all of what you say is derivative of juvenile naivete concerning sex. The fact that an adult mind superscribed additional intricacies does not redeem the puerile concept from being what it is: a flower penis. It's not a "metaphor," by the way, which would require that it represent something else. I don't even think I could give it the literary nomenclature of "simile." One might argue that the
whole of the books are a metaphor, but the flower-penis? That's just a juvenile sex-fantasy gone awry.
And we are not just talking about a "penis that spits acid" here: the entire body chemistry of the Wraeththu is poisonous to humans, one side effect of which is that, yes, sex with men or women would be lethal (which is why it isn't done except by murderers and diabolists of the worst kind).
In her own words:
The Wraeththu hated mankind. They were different; on the inside and on the outside. Hungry, baleful fire smouldered in their skins, you could see it looking out at you. They drank blood and burned the sanctity, the security of society, infecting others like a plague. Some even died, it is said, at their touch.
That does not bespeak a society that looks upon a
rare few who are "murderers and diabolists." It nearly states that such is the base condition for the entire group of people. Humans become less to them than they are to vampires. At least to vampires, humans are "cattle."
Once you have completed your defense of this group, perhaps you could next defend the unabashadly loving fan-fiction devoted to pedophiles, rapists and serial killers?
And "sex-fantasy"? Only in the sense that alternative sexuality forms the central motif in the books. There are more explicit scenes in Harlequin romances: if you expected the novels to consist of one chapter-long copulation after another, you'd be sorely disappointed. The characters need the energies released through intercourse to survive, true, but what bedroom antics there are mostly take place off-screen.
It's a fantasy...
It's about sex... (alternative or not, splattered on the pages or not, graphically described or not)
Thus, it's a "sex-fantasy."
Comparing it to other, more mainstream, sex-fantasies does not erase the fact that it
is a sex-fantasy. Puerile, immature, debased and surrounded by the affectations of rape, pedophilia and serial-killing does not exactly make for a "redemption" in my eyes.