It is common to hear questions like this from Christian apologists in an effort to prove the existence of objective morality. C.S. Lewis and William Lane Craig both made versions of it, and I received a version of it from Myles and SuperLutheran of the Godcast.
The short answer is “yes, rape is always wrong”… but unfortunately for apologists, this actually doesn’t tell us anything about objective morality.
The problem with a term like “rape” is that the term itself is a judgment category. Rape is a subcategory of “sex” — specifically, the kind which we all agree is, by its nature, bad (it is not the only kind of bad sex, but among the higher bads).
By way of illustration, think about the difference between these two questions:
Is rape always wrong?
Is sex always wrong?
Notwithstanding those Christians who would affirm the latter, we can already see the trick in the set up just by asking the proper question. To get to an objective standard of morality, we would have to describe actions categorically, not turn it into a tautology trap by beginning with a subcategory of a broader action which has already been separated — by humans — from the rest.
It isn’t made any easier by the fact that “rape” isn’t a clear category. In the West, “rape” has to do with consent, including the statutory possibility of consent. A 25 year old man having sex with a 16 year old woman is rape in America, but is not rape just south of the border in Mexico. Often times, a 25 year old woman having sex with a 16 year old man is not considered rape. And what of “consensual rape?” where a woman expresses interest in a semi-violent fantasy, and a man fulfills that? Is this morally wrong? Some might say yes, but it seems less categorically so.
The same problem exists with the parallel question “is murder always wrong?” When we replace “murder” with “killing,” it suddenly becomes less of a dunk on subjectivists and alleged moral relativists, and turns into an actual question, with some theological answers which put the Christian at odds with the cultural norms, rather than trying to leverage cultural norms for the purpose of evangelism. There are strong strains of pacifism and celibacy in the history of Christian thought. From a biological perspective, one’s starting intuition should be that sex and killing are categorically permissible, at the very least in the contexts of self-defense and procreation.
I think many people home in on this question because there is a kind of fear that if our moral values lack some kind of objective backing, they will bend and break against the tide of a short-sighted and hedonistic culture. Putting aside the truth of the matter, I think the concern is misguided — objectivity adds nothing, except maybe the hope that one might be able to browbeat another in debate by appealing to a shared higher authority. More often than not, this browbeating often just makes the other side dig in deeper, especially in the face of an apparently air-tight argument. But for an individual trying to live a moral and virtuous life, declaring a subjective value to be something objective adds nothing. Subjective values are sufficient to live by. They have to be, because even if objective values did exist, all we would have access to would be subjective interpretations of them (which might be why our history is dotted with so many civil wars between factions of the same religions with the same objective beliefs).
But there is also a danger in asserting that values are objective: it opens up those values to the inquisitorial elements of a new religion — science. Science is better at investigating objective claims than the church has ever been, and claiming that “beauty is objective” has already lead to a beauty-destroying path of scientific inquiry.
This, of course, would have happened without the claim too, but taking on Science head-on and asserting that beauty, justice, and freedom are subjective, and not the proper subject of scientific inquiry. This would put Science on the defensive, perhaps forcing it to explain the scientific origins of its own highly-developed ethics codes (or is there some foundation of value beyond objective truth?), and stemming the flow of its Utilitarian Skinner-Box approach to public policy from our current culture.