If homosexuality is 'natural' because animals do it, then rape is 'natural' too. That's why people don't like it, because uncomfortable ideas aren't critiqued, discussed etc anymore, they're shouted down and shamed.
To think that the sexual behaviour of non sentient species should have any bearing on humans is ridiculous (in either the positive or negative sense). Why can't these idiots just study something dispassionately without projecting their own political bullshit on it. A male giraffe that courts and mates with another one is no more or less important than a seal raping a penguin.
*Edit*
Posted without checking your link, thought you were referring to another contempary article I saw about rape in nature.
In regards to rape as evolutionary biology then I am even more astounded that people can't see that in humans, as in many species, that forced sexual intercourse leading to procreation was a successful mating strategy at various times in history and those who are predisposed to this mating strategy would pass those genetics on to their offspring.
Argue the science, not the 'feelings'. Rape is not born from a culture of misogyny, in fact the rapist (even the accused rapist) is one of the most reviled figures in society and the criminal most likely to be punished by vigilantes or violently attacked in custody.