The myth of Apemosyne seems awfully cruel, even compared to other cases of sexual misconduct in the Bibliotheca. Unlike other cases of gods raping mortal women, the princess didn't even bear a hero to Hermes, since she was beaten to death by her own brother soon afterwards. Is this another case of different set of values regarding godly rape, or is this myth supposed to be an intentionally bleak counter-example of how male relatives should react to violence against their family?
I'm really not sure. It is interesting because Althaemenes comes across as a rather noble figure, especially in the account of Diodoros of Sicily (59.1-4): he leaves his home out of concern for his father, founds a temple, is held in high regard by the inhabitants of Rhodes, dies of grief after accidentally killing his father and later is honoured as a hero because of an oracle.
The account from the Library of Apollodoros also has some of these details, but complicates Althaemenes by mentioning his treatment of his sister. Given how unambiguous the sexual assault is and the fact that Apemosyne is killed without the god intervening in any way makes it unlikely to me that Hermes' conduct would have been considered anything but negative. As for the way the brother reacted, it seems very harsh even if his sister had engaged in sex out of marriage of her own accord, but Aeschines (Against Timarchus 182) brings up a legend in which a young woman is locked up in a house together with a horse that is meant to end up killing her by her father as punishment for having a lover before marriage. The punishment is not presented as a bad thing, but as a demonstration of the intolerance of shameful conduct among the Athenians. Immediately after this he describes a law of Solon according to which women guilty of moicheia were not allowed to adorn themselves or attend public sacrifices; if caught doing so, any man was permitted to humiliate and even physically abuse them, short of murder or maiming.
So I don't know. It might have been considered tragic that Althaemenes killed his sister for a crime she didn't actually commit. What we can say is that he suffers no consequences for that act. He just ends up fulfilling the prophecy he was trying to avoid, similar to other figures and unrelated to his prior actions.
