Because your proposed solution to possible working awkwardness is not 'growing a pair', it's making an already awkward moment even more awkward, or possibly scary. Now not only does she have to deal with your blustery bravado in the moment, she also has to worry about unwanted advances in future situations where you might be alone together.
What you seem to think is candid, useful communication is anything but.
If you are attracted to someone you're going to be working closely with, there is a time-honored approach for dealing with it. You flirt. If you're good at flirting, then it is non-serious and does not create a threatening atmosphere. It shows off your positive personality qualities and hides your negative ones.
Most importantly, it gives the lady in question an out if she doesn't want to go there with you, she simply doesn't respond. If she doesn't respond to your flirting, then she's not interested and the stand-up, manly thing to do is to stop flirting, and carry on your working relationship in a completely professional manner.
> If you are attracted to someone you're going to be working closely with, there is a time-honored approach for dealing with it. You flirt.
Oh come on, with the romance and everything. Don't you see that our friend yummyfajitas here has bodies to fuck?
He is really just trying to help society to a more sophisticated and unfiltered understanding of his urgent needs and minimal concern to the accidental personality that may be contained in those bodies he desires.
Back before he was ushering in his new era of "rude honesty", it might have taken weeks to figure out whether a body is available to be penetrated by his penis. Now we can all rest assured that he will save himself and the bodies he surely deserves to boob-touch to his hearts content (if the feeling is mutual, of course, he's not a monster!) a good chunk of time.
I think you're on to something with the 'flirting' thing. Unfortunately, most of us probably don't know how to very well- especially when it comes to reading the other person's intent.
It is OK to get things wrong, too. I mean, ideally, you'll look for romantic partners outside the workplace, but if you must look at work, it can still be OK. If you flirt, you think the other person is flirting back, you ask them out, and they reject you, that is neither sexual harassment nor a grave offense.
Example approach (in our scenario, this is toward the end of a workday, which is when you would want to do anything like this): "Hey, I've been having a lot of fun working with you, would you want to get dinner together sometime?" "Oh, I'm sorry, I'm [not looking for a relationship right now|seeing someone else|not interested in you that way|...]." "Oh, shoot. Well, I'll see you tomorrow then." (Go home.)
It may be a little awkward, but if you do things respectfully, then it will probably not ruin the working relationship. And more importantly, you'll have flattered the person you're working with, not creeped them out or made their workplace environment hostile, not cemented yourself in their mind as a total asshole, and not put yourself at risk for getting fired for harassment.
Of course, you will never do this to one of your reports or their transitive reports unless you would like to lose your job. Only peers or members of another org.
I don't know that it's "vile and hateful", but it might make things uncomfortable.
Revealing that you have sexual feelings for a person with whom you're nominally supposed to be forming a sexless, professional relationship will either lead down a path to sexual or romantic connection, or else make things tremendously awkward. That's not a sexist act, necessarily, but it could lead to a conversation with HR.
