In other words, the point is that sex is put into a separate sphere of activity from other ordinarily-pleasant experiences and given a dignity which is not special to those other activities. (This is not particularly tendentious: most cultures have, say, hygeine laws which are important to follow but it's hard to identify the exact reason "why". Egg on your face is "dirty". Will it hurt anyone or cause you to contract or spread disease etc.? No. But it's still dirty and it's still important in our culture.)
The gap from sexual harassment to rape is therefore not, say, violence, but the escalation from uncouth groping to uncouth sex. The fact that there is a narrative where she looks out upon her options and says, "okay, I will fearfully give this man a blowjob rather than give him the middle finger and prepare for joblessness" -- one where she somehow rationally "chooses" sex as her "best option" -- is moot if sex is fundamentally privileged by the society you're a part of. The problem is that the "rape" has essentially happened (it's happened as a conspiracy, say), by the time that that "choice" has to be made.