“Now, it makes sense to me that the more extremely sexual and/or uncomfortable a piece of clothing, the more likely it is (in general) that the woman is wearing it for the purposes of sexual attraction; so a catsuit is more likely to be donned for sexual purposes than simply an attractive skirt. Are we agreed thus far?”
“Different families, countries etc have different sexual climates, and these can be hard to infer from simply looking at a woman. Again, would you agree with this?”
To some extent, what constitutes provocative attire is culturally variable. Islam is a case in point.
“Body language, context and so on are therefore useful indicators to a woman's motives. Agreed, again?”
“Do you think it's ethically permissible for an unmarried man to look at an umarried woman for the purpose of sexual enjoyment?”
i) That’s an interesting and complicated question. Traditionally, the locus classicus is Mt 5:27-28. However, most readers don’t really exegete this text. Instead, they consciously or unconsciously plug their own experience into the text. So this becomes an exercise in mirror-reading.
ii) Not that personal experience is entirely irrelevant to the interpretation of Scripture. Like communication generally, Scripture takes certain things for granted on the part of the reader. However, experience shouldn’t become a substitute for other exegetical considerations.
iii) This passage has its background in the seventh and tenth commandments. As such, it has specific reference to adulterous covetousness.
Mental adultery would either involve someone's spouse mentally seducing a single person or else a single person mentally seducing someone's spouse. Something along those lines.
Most readers equate Mt 5:27-28, not only with mental adultery, but mental fornication. However, that’s broader than the OT background which informs this text.
In the OT, adultery and fornication were not equivalent. Whether there’s such a thing as mental fornication goes beyond this text.
iv) That leaves us with three possible options:
a) Mental fornication is morally impermissible on the basis of other passages of Scripture, or other Scriptural principles.
b) There’s no such thing as mental fornication.
c) It’s permissible for a single man to fanaticize about a single woman (or vice versa), but we should avoid that on prudential grounds.
d) It’s permissible for a single man to fanaticize about a single woman (or vice versa) as long as certain restrictions are observed.
v) On a related note, while sexual attraction is involuntary, sexual imagination is generally voluntary (an exception would be erotic dreams).
Using our imagination involves an act of the will.
A single man might imagine taking a single woman out for a date, without imagining a sexual encounter.
vi) Apropos (iv)-(v), I’m not, as of yet, taking a position on which hypothetical option is ethically correct. I’m simply drawing attention to the complexity of the issue, since this is often overlooked in Christian discussions.
Generally speaking, I think it’s probably the case that single men and women are allowed freer play of the sexual imagination than are married couples (or couples engaged to be married). Married couples can only fantasize about each other. Single men and women are not quite as limited in this regard, for they have yet to enter into a committed relationship (e.g. marriage).
vii) The Bible also uses a certain amount of sexual imagery. This involves a deliberate appeal to the sexual imagination of the reader. And the reader is not married to, or espoused to, the anonymous sexual object. (I say “anonymous” because Scripture is using generic sexual imagery.)
So we can’t rule out all use of anonymous sexual imagery.
viii) At the same time, when Scripture uses sexual imagery, that’s directed at marriage. It celebrates marriage. Or it editorializes against the extramarital abuse of marriage. Or it uses sexual imagery as a spiritual metaphor, for good or evil.
So this is not meant to be a permanent alternative to conjugal relations.
ix) On the other hand, Scripture also recognizes special cases in which an individual is not at liberty to marry. But that’s exceptional.
I’ll revisit your second question in a separate comment.