"Deviant" needs some reference point, but there is none in science when morality is not objectively there but only relativistically invented by humans.
Deviance can be defined by a given moral system, but in the US, Europe, and a number of other places which share the social scientific framework, it typically isn't. A moral system means you can call things "wrong", "bad", "sins", etc. Deviance automatically
does have a reference point, because it quite literally refers to behavior relative to norms, and as it is impossible for any social group to exist without these, there will always be a range of behavior which can be deemed within the "normal range" (in particular, as most societies today are large enough that behaviors and views tend to approximate a normal distribution, it is relatively easy to locate a range to use as a reference point).
The fact that it is relativistic only means that (barring word from on high or something) deviant behaviors are immoral only to the extent that they a given society holds them to be so, and that deviance itself is not fixed but at best is grounded in commonalities shared by all humans (e.g., language, some socio-political system, etc.; Pinker's
The Blank Slate includes as an appendix a list of universals, although I'm not sure how many would agree with certain entries).
Although what constitutes "rape" changes depending on the culture and time period (it was not that long ago that a husband couldn't rape his wife, because she had no right to refuse), it has always been considered deviant, and is certainly deviant today, whatever philosophical stance one wishes to take on the applicability of the term "morality" granted that morality is relative.