It is an option. In fact, it sounds like that is nearly what Ms. Fowler did -- she reported the interaction to HR (who informed her supervisor but took no action) and then she kept working there.
In my opinion, if the person who has been propositioned by their boss WISHES to just say "No" and let it pass, then they are welcome to do that. Some people are comfortable handling that sort of thing. But I would NEVER want to suggest that a person propositioned by their boss OUGHT to simply say "No" and let it pass. Very few people would be comfortable doing that and everyone should be entitled (are entitled, by law) to be free of requests for sex by the person with the power to promote, demote, or fire them.
Only a sociopath would actually fire you for turning down a proposition, but this is your first interaction with the guy, so you have to consider the possibility.
There are many reason why someone would be a pain to work with honestly. I could imagine someone insisting on people going to drink after work being a pita for a muslim for example, or a guy talking all the time about politics and having different views than myself, etc, etc. But it seems like sex is handled extremely differently than the rest, and i'd like to understand if, in practice, there are reason for that (other than the subject itself being extremely sensitive in the US compared to some european countries, for example).
"sex is handled extremely differently than the rest ... [is there] reason for that[?]" I mean US internet culture is the place where this baleful notion of the "friend zone" exists: men who complain bitterly that being nice to women does not secure for them a sexual relationship. Denigration or retaliation following sexual rejection is a well-documented practice. From what history do you think sexual harassment laws spring? Women fought for them because they survived regular abuse, manipulation and retaliation from men (especially superiors). Have you read any of this history? for example: http://www.csmonitor.com/USA/Society/2011/1114/The-evolution...
It says something about the culture of the company that a manager feels unfettered to ask his direct reports for sex so boldly, i.e. without fear of consequence. I'm shocked you do not see this.
There's a power relationship between reports. Most companies have explicit guidelines that prohibit romantic relationships along the management chain.
And that leads to a country where every manager is absolutely terrified to be accused because they know they'll be automatically guilty.
In the OP case, the manager clearly behaved completely foolishly, but i have actually met people in some offices that were into open relationships, and talked extremely freely about sex, just like any other subject ( though he did have some weird behaviors, but it didn't prevent people at the office from working with him). I wonder if that Uber guy wasn't like that.
1. He was propositioning her; not just "initiating a topic".
2. That person was her manager, which changes the picture altogether (see this comment by 'calcsam: https://news.ycombinator.com/item?id=13682117)
to me, the term "harassment" means repetitive, morally painful actions from a boss to his employee. Obviously the guy has a huge problem with his sex life, but why report to HR instantly , instead of trying to see if the problem is that big and can't be solved by a person to person conversation, like grown up, first ?
EDIT : i'm not trying to be a jerk, and justify the behavior of that guy. I'd just like some woman working in tech in the US to explain to me what's wrong in my scenario.