I don’t think the cause is either of your proposed candidates. Instead, it seems to me that the Madonna-whore complex is what happens when a prudish ideal meets the naked truth. The prudish ideal is a bizarre picture of women in which they are maternal but non-sexual. The naked truth is that typical men and women both like and want sex—and not just sex, but good and mutually enjoyable sex.
If one accepts the Victorian view that men are creatures of desire that women must hold off and tame, and that women have sex only for procreation and to keep their men in line, then any woman who enjoys sex must be a whore and unworthy of marriage. But if the naked truth is that the average person seeks out good and mutually enjoyable sex, then any woman who fits the virginal ideal is unfit for a long-term relationship.
It gets further complicated when you realize that men are also subject to strict social roles in sexist societies. While they may not be subject to the sorts of institutional oppression that face women, their social options are often much narrower than those allowed to women. That is, there is often a very narrow picture of what is masculine with everything else being described as feminine.
Sexual prowess is typically part of “being a man” in such societies. But if you can’t have (mutually enjoyable) sex with your wife (who must be virginal and maternal), and if you can’t have sex with anyone else (yay, monogamy!), then you’ll have to go find those who society deems to be nobody (the whores). They don’t count, of course, because they are women who have abandoned femininity by having sex for pleasure.
This situation does not arise out of the actions of women, yet it is no more a function of ordinary male psychology. It is a result of the intense cognitive dissonance that comes from instilling incompatible values in people. Historically, these values have been promoted by groups looking to control others (not necessarily as rulers) by making them feel guilty or shameful with regard to their biological drives.
Sex, as it turns out, is ideal for this sort of manipulation. You can make people feel guilty about any of their drives, and there are certainly those who shame others for their eating habits, their sleeping habits, and so forth. Sex, though, is the only drive where the desire can be made to seem disproportionate to its function. It’s hard to argue that daily eating and sleeping are suboptimal, but daily sex may seem unnecessary if you think its only function is reproduction.
Reproduction, however, is not the only function of sex. It’s not even the only social function of sex. Even if we believe that reproduction gives as a complete evolutionary explanation of why sex came about, it remains the case that sex changes relationships and promotes—though does not guarantee—closeness and cooperation. Properly done, it is psychologically healing and relaxing. This is one of the reasons it is such a terrible thing to take advantage of or use as a weapon.