The problem is you go home, but then you come back to work the next day.
I am a professor of statistics, and have encountered lots of issues surrounding relationships and harassment involving colleagues as well as once myself.
Based on these experiences, I agree with you for the most part, but am not sure even that is workable advice, unless you want to create an cold, inhuman environment. And even then it raises lots of thorny issues that you might not anticipate.
I can say from one, personally impactful experience, for example, that "talking for hours if you need to" at work, with someone you work with one-on-one for hours daily, can lead to, say, a mentee declaring feelings for you. Maybe this talking started under pressure from other colleagues and students to help the mentee feel more comfortable because of concerns about how they're feeling in general. And because that individual might be a brilliant, amazing individual you've found you share a lot with, after enough time, you might develop feelings for that mentee too, even if you never started out with an inkling of that when you started reaching out to them. The immediate response, you think, is "well, tell them these kinds of things are inappropriate and leave it at that." Ok, but then, without any further context, does that shame the mentee and lead them to believe that their feelings are abnormal? Do you tell them that it's normal, you have feelings too, but nothing can happen as a result, it's inappropriate to pursue a relationship? In that case, even if nothing physical happens, it might lead to severe complications later, purely emotionally, as both of you deal with the consequences of knowing you have strong feelings for each other but nothing can happen as a result. Do you say nothing at all? After all, the mentee confessed feelings for you without you saying anything to them of that sort, and that didn't stop them from telling you that they have feelings that way. Will they try to escalate things if you don't say anything? Do you reach out to colleagues? Will that shame the student or damage their reputation?
Take this a step further. Let's say you do somehow prohibit males and females from becoming close. Do you prohibit purely platonic same-sex relationships from being close? Is it say, sexual discrimination when a female faculty member has her (non-romantically involved) female, but not male, students over for dinners regularly, to chill and watch movies or have small gatherings, shares hotel rooms to save on costs (for cash-strapped students at expensive conferences)? That is, after all, discriminating against male students on the basis of gender. Or are they just being caring and friendly with their students, and careful in avoiding complications with members of the opposite sex? What if a female faculty member never takes male mentees? What if it were a male faculty and male students? Isn't that the "old boys" network? Where do you draw the line? When does differences in closeness of relationships become gender discrimination?
Unlike you, I do think there's lots of gray areas, and I see it as an unavoidable consequence of humanity. I kind of agree with you that ideally, you should just keep work relationships impersonal, but I think that's really unrealistic in practice. What worries me is this kind of blanket idea that any feelings or sexual behavior or relationships between coworkers or supervisors and supervisees is always the result of some maliciousness or failing or something on someone's part. It seems there needs to be a more nuanced approach to these things, or some more realistic discussion that recognizes people do have feelings for one another, especially those they are in regular contact with, platonic or otherwise.
I've heard of all sorts of stories in this area involving other students and faculty, from advisors basically sexually assaulting students, to advisors who end up marrying their students and ending up in very happy, healthy marriages. There's also things like students and advisors who are close and end up having sex at a conference when they are both completely intoxicated and both regret it later.
I guess what I have difficulty relating to in the published story is making physical sexual advances on people who you aren't close to, out of the blue. I have difficulty relating to that, but then again, the workplace context doesn't matter. I wouldn't do those things at a bar or someplace else either.