Among primitive peoples, though in the media it tends to be often portrayed as an issue supposedly only afflicting the Islamic world, you will see another double standard, I am talking of course about so called "honour killings".
In primitive societies in general (and yes, these things extend far beyond the Islamic world and are typically observed in hunter-gatherer peoples, whose way of life is far more reflective of the environment in which our ancestors evolved than is the 21st century western world), females who violate the sexual norms of their group are often put to death, and not only that but the norms constraining males are far more... lenient... to say the least - typically moreso in practice even if not by principle (e.g. Islam prescribes the death penalty for both male and female adulterers yet for some odd reason, the victims of that law seem to be disproportionately female).
And I am not just trying to attempt to deflect your issue by changing the subject to double standards that victimize women. The aforementioned phenomenon and your "double standard" in fact have the same ultimate, that is to say evolutionary, cause.
It has to do with a particular sociobiological property of the behavioural patterns of homo-sapiens, one where the sexual competition over mates is conducted primarily by the males over the females. It is female sexuality that is the valuable scarce resource in the world of homo-sapiens. This is why the vast majority of human societies throughout history have been polygynous, why female virginity has been and continues to be virtually sanctified in many parts of the world (but little is said about male virginity), why daughters are far more likely to end up being pestered about their relationships and many, many other peculiar "double standards" concerning attitudes and reactions to the behaviour of the sexes.
And yes, this is the ultimate reason for why male and female rape, even if the later is legitimately done (i.e. the female somehow disables the male as sometimes happens), evoke very different reactions from most people. The proximate reason is that, unlike male rape of females (which would probably have been a rather common form of primitive human behaviour, in fact see below *), a female raping a male simply doesn't trigger those explosive emotional tribal reactions the reverse does (in primitive societies rape and female sexuality-related issues in general are often a cause of things like family feuds and even tribal warfare, a testimony to the irrationality of it all).
A bit more than a decade ago, the biologist Thornhill and anthropologist Palmer made the feminists literally berserk with their work "A Natural History of Rape: Biological Bases of Sexual Coercion" in which they set out to deflate the popular feminist wisdom that rape basically has nothing to do with biological human sexuality whatsoever and is instead about "power", i.e. an expression of the nonexistent "patriarchy". Thornhill and Palmer may have ventured a bit too far in speculative waters in their hypothesis that rape might even be "adaptive", but if sexual behaviour does not have something to do with evolution, then frankly nothing does.
