Morality is a used term that is commonly applied to levels of activities in varying degrees of disapproval. We need a much better word, or a set of words, but then we would have to agree on what morality is and that's the big public struggle. Sex is considered a moral issue in the public. Sex is never immoral. Force or fraud, that is immoral.
Rape is immoral because it is assault.
Whether or not the rapist completed the act is immaterial. It's the use of force that makes it a crime. Consenual acts that you personally would never engage in are not immoral. Consenual is the determining factor, not your personal distaste level. The area where libertarians might have disagreements with me is in the area of fraud.