I am in fact referring to the same issue mentioned very briefly here. I am dreadfully sorry for discussing the subject.
The issue itself is Larry Niven's essay here. Not the subject of the essay as much as the essay itself. Just to make that clear. I'm planning to tear apart the assumptions of Niven's essay. Nothing personal, I just want to tear it apart because it's not as clever as it makes itself out to be. (Granted, it's nearly forty years old, and is thus quite dated, but still.)
I'll address it point by point. (If you've never read it, you might consider skimming it.)
I. Superman can't be, um, attracted to human women.
Blatantly false. Blatantly. As we (i.e. the Internet-going populace) know, lots of people can, um, be attracted to mere images. A living creature that resembled the opposite sex of one's own species that closely would be more enticing, even if s/he shrieked hostile things in an alien tongue at your mere presence (indeed, for some this would be a plus).
And Kryptonian relation to humanity is questionable. Could be there, could be (but probably isn't) pure coincidence. But Kryptonians are hardly the only very humanlike aliens out there in DC, and we know that at least some of those can (probably) interbreed with both humans and Kryptonians. (We also know that as of ~3000 AD, Daxamites can interbreed with humans. Since Daxamites are only a half step away from being Kryptonian themselves...)
II. Superman would lose control of his body during... you know.
Oh-ho, and now Niven's contradicting himself. Earlier, he said that Kryptonians can't be compared to humans, and now he's saying they're just like humans? Foul! Foul!
At any rate, I tend to think that Superman has a lot of self control. I mean, during the time period Niven was writing in, Supes had "super ventriloquism" as an innate power because of uncanny self-control! No training, no nothing, yet he could still do something most people needed a combination of aptitude and training for!
III. Superman would lose control of his carnal urges during... you know.
I think I've already addressed this, haven't I?
IV. Superman's... climax... would be naturally lethal, with the force of a gunshot.
Bleah, Niven. Bleah.
I'm not inclined to think this is true, primarily because there's no evidence that Supes has abnormal blood pressure. Perhaps his heart is a bazillion times stronger than mine, but that doesn't mean it pumps his blood around harder. And the same may or may not be true of all bodily fluids. I'll leave it at that.
V. Kryptonian sperm will have all of Superman's powers.
Okay, we know that, in the Silver Age, all Kryptonian animals had cells that gave them the same powers as Superman. That doesn't necessarily mean that individual cells of Kryptonian animals would have Superman's powers. Particularly, since sperm lack most organelles (the structures that allow most cells to function), I'm inclined to think that, while Supes' powers do originate on the cellular level, sperm cells would not have the necessary structures to grant them these powers.
Most of the consecutive points work on the supersperm assumption, so I'll skip ahead.
XI. Superfetus will kill the human mother.
Heh. Okay, this is not necessarily true either. In the Golden Age, little Clark Kent was strong from the moment he arrived on Earth. In the Silver Age, well, I'll assume it was fairly similar. In the modern post-Crisis etc. universe, it's generally agreed that it took a long time for Clark's powers to emerge-not until he had roughly hit puberty or after. Why does it make sense for Superfetus to harm the mother?
Also, it's clear that the modern penchant for magic red sunlight lamps cancelling out Superman's powers was not yet in vogue when this was written; otherwise it'd be very simple to answer this problem for even Silver Age Superfetus.
Also, I'm not even touching point XII. Superman's no Zeus. (Explanation for that remark here, if you don't know enough about Greek mythology.)