I think some folks might be under the impression that a sensitivity reader is to ensure nothing in your work is upsetting to sensitive people. That's not the case.
Basically, it's someone who has first-hand experience with an element in your work. This can be experiences tied to race, gender, ability, class, whatever. The idea is that you don't have first-hand knowledge of a topic (i.e., being the opposite gender), so you want the perspective of someone who lives that reality to ensure nothing you write is blatantly false or perpetuates harmful ideas.
For example, I once read over a script written by a male peer. After reading the script, I had to warn him that a lot of his female characters' behaviours were pretty off-putting or just... bizarre. Some of the writing just flatly didn't ring true to me or the experiences of any women in my life. Some of it was actually pretty upsetting and capitalized on negative portrayals of women. It was all stuff that, as a guy, he hadn't given much thought to because his experiences were different.
I brought it up to you with regards to the topic of sexual assault in your story. If you don't have personal experience with sexual assault, it's very difficult to know when you've crossed a line. I'm guessing the last thing you want to do is accidentally mock or fetishize sexual assault/rape. But myself and a few others were concerned when words like "brush it off" and "joke about it" were used and revealed that you may not understand of the gravity of this topic.
In any case, I don't think people should be barred from writing different perspectives unless they're approved by someone else. BUT-- if you're trying to tackle a touchy subject that's not in your realm of experience, it's a good idea to consult with someone who has first-hand knowledge. Otherwise, you could potentially alienate your audience or perpetuate damaging stereotypes without knowing it.
