Seems to me your question poses what is known as a false alternative. I see no reason why a parent cannot help to inform a child about gender norms, so the child can understand these norms, while still making clear that such norms are really not necessary, not appropriate, and stifling. Don't we try (well, those of us who are decent folks, anyway!) to do the same with racism and other forms of prejudice?
(1) Are the psycho-sexual aspects of ourselves fixated from a relatively early age, so that "turn ons" [what we find sexually arousing] are conditioned if not unalterably then in some way that fixes in ourselves certain ideas about what it is for something to be sexual [to be sexual or to be sexually arousing?] in nature?
---Some philosophers argue about this. See Ed Stein's edited book, Forms of Desire, on the "essentialism" vs. "social constuctionism" debate. The question appears to be one for psycholgical theory (see Freud, e.g.). Perhaps what philosophers have been doing is to reflect metapsychologically on the issue. Some experimental research has been done on to what extent and how certain sexual desires can be modified (e.g., in the case of pedophilia and rape). See also Sylvere Lotringer, Overexposed: a study in behavioral modification through overstimulation and habituation. (The idea being, if one gets too much of a stimulus, one gets bored of it. Married couples know this well. Works to some extent on other, nonmarital, sexual interests.)
(2) Should considerations about this act as impetus to revise any aspects of the media and popular culture, including of course, pornography, which is one of the largest domains of media-culture despite being confined to less blatant forms of presentation (than, say, advertisments for "Big Macs")?
---Again, a question dealt with by a bunch of social psychologists, e.g., Malamuth, Dinnerstein, Check, Zillman, and others, although philosophers have contributed by asking questions such as: can psychological science really answer questions about the impact of pornography (and advertising), and what are the normative implications, if any, of the (purported) harmfulness of various types of media?
(3a) Finally, I have the idea that cyber-porn (and to a lesser extent all cyber-sex) is covertly homo-erotic when men use it to get off on "straight" screen sex.
---It is probably true to some extent that some males who watch heterosexual porn are primarily interested in the workings and doings of penises. Whether that means they are covertly (or overtly) homo-erotic (homosexual? gay? bisexual? pansexual? polymorphous? etc.) depends exquisitely on how we understand the concept of "sexual orientation." Further, the unconscious is a funny thing. We also know from Kinsey and other studies that on the scale from 0 to 6 (0 = pure het), many more men are 1 and 2 than we ordinarily think. So why believe that the homoerotic component is always or mainly covert?
(3b) This isn't entirely true, sex is sex and breasts are breasts, but the fact that a machine which could be (not unfairly) called a "boys toy" is being used as the platform for a mathematically constructed system of media exchange (viz. the world wide web) that was developed primarily by men.
---So? What does this have to do with the homoeroticism, latent or patent, of cyberseuxal images and the responses of men to them? I am not seeing the connection here.
(3c) Crucially, the sex scenes themselves are heavily male edited, and in many of them there is little left of female sensuality
Grossly false; take a better, more representative look at pornography-- not just the kind you like. :)
(3d) (and, perhaps not coincidentally, a hugely disproportionate screenage of male/female genitilia as compares [compared] to sex in the flesh).
---Oh? Again you misrepresent porn. Futher, the last time I had sex (years ago, I must admit) the time- or attention- proportion of male/female genitalia was large (including oral sex, mutual masturbation, not only coitus), although not exclusive---as compared with what? Ozzie and Harriet? The perfunctory domestic kiss that Kierekegaard rightly made fun of?
(3e) Doesn't that amount to "getting off on" a male conception of sexuality (or one form of it), and if so, can that count as homoerotic?
---Nah. "Getting off on" a male conception of what sexuality is, or is like, or should be, or would be in ideal circumstances, has nothing to do with the images so constructed being homoerotic or appealing to homoeroticism. Indeed, quite the opposite, if the make makers of porn, employing a male take on sexuality, or male hopes and wishes, are heterosexual. You are reaching, stretching, for something that is just not there. Still, it is good to stretch, as long as we can put our muscles back where they belong afterwards.
Most philosophers now recognize a distinction between the biological category "sex" and the social category "gender." One's sex is determined by a collection of biological factors that typically (though not always!) go together: chromosomes, anatomy, and hormones. Gender is the social role a society assigns to persons on the basis of their sex: the set of expectations about behavior and appearance deemed appropriate for someone of that sex, and a system of rewards and sanctions that enforce conformity.
The sanctions that I speak of can take many forms. There can be explicit laws or regulations specifying which roles can be performed by males and which by females, with punishments for violators. But there can also be informal or tacit conventions that are extremely effective. A man who wants to get ahead in the American business world will not wear skirts or lipstick, whereas a woman in the same milieu will do exactly that. (Check out "Dress for Success" at your local bookstore.) More seriously, women who violate social expectations about sexual behavior, for example, are often faced with loss of social standing, and may even be regarded as fit objects for violence and rape.
Because these social forces are so effective, they create real and observable differences between men and women. Consider hair removal: current American gender norms dictate that women shall have no hair on their faces, underarms, or legs. But women do have hair in these places. (Yes, Virginia, there is a bearded lady) To conform to the "hairless" norm, they spend millions of dollars shaving, bleaching, waxing, electrically zappping, and dipilatating it off. The result is a real regularity: American women are much less hairy than American men.
But here's the kicker: although conformity to gender norms often takes a great deal of deliberate effort, it's part of the norm that this effort must be invisible. So, to stick with my example, many men are CLUELESS about what women do, and have to do, to remove hair from "unwanted places." The existence of the norm, therefore, creates not only an observable regularity, but the impression that this regularity is "natural."
There's a further complication: because the impression is fostered that these engineered regularities are "natural" -- i.e., not the result of deliberate human effort -- the content of the norm itself incorporates an ideal of naturalness: the more a woman conforms to gender expectations (regardless of how much effort and frustration this actually causes her) the more "natural" a woman she is thought to be. A woman who announced that she'd like to have children, but would prefer that her husband raise them herself because she's just not that into babies and toddlers, is regarded in contemporary American society as not just unusual, but as "unwomanly." Similarly for men -- the man willing to marry such a woman had better be really into sports, or he's a social goner.
So now I can answer your question: yes, there are differences between men and women. But given the efficacy of gender norms, no one could have any basis for attributing these differences to differences in "natures" between men and women. Indeed, the whole nature/nurture controversy is vexed, and generally embodies multiple confusions -- not the least of which is the idea that a property one has "by nature" cannot be changed. The important question, and one that can be answered, is whether the nearly universal practice of slotting people into gender roles is a good one or a bad one. The jury is in on this: gender roles are in fact, and probably are necessarily, hierarchical and oppressive. They lead to unjust social divisions based on morally irrelevant biological facts, and should be abolished.
If you want to see these points developed in more detail, let me recommend The Politics of Reality by Marilyn Frye. Enjoy.