There's a scene in When Harry Met Sally where Harry and Sally are debating the state of friendships between men and women. Sally says she has tons male friendships which she says are purely platonic. Harry says, "no, they probably all want to sleep with you."
Sally gets all disgusted and is like, "what? Do you want to sleep with all your attractive female friends?" Harry says, "no. I want to sleep with the unattractive ones too."
More or less.
To the defense of the male population, Harry does not speak on behalf of all men. But it's also safe to say that he does reflect a large majority of the biological and innate male brain.
But what about girls?
A truly platonic friendship is when both male and female see each other as nothing more than FRIENDS. Almost to the point of brotherhood/sisterhood. It's so platonic that the thought of sex or any romantic notion should almost be deemed illegal. Yet, you think the world of them and love them like your own blood.
This level of friendship usually takes a while to achieve. I believe all male/female friendships start off with an ambiguity -- there's often a probation period to feel out where the friendship stands. Of course, this ambivalence becomes clear if one person isn't single or is gay. That helps loads! But once this alleged hurdle is crossed, there are endless possibilities in terms of what kinds of platonic friendships can form. Hurrah for the friend zone!
But what about the friendships that aren't 100% platonic but are on the cusp of friendliness & flirting? Some friendships never ever quite make it to the friend zone, whether it be a.) the level of innuendo constantly maintained or b.) the tension and/or attraction that's never quite dissipated or c.) one or more person is always horny and has sex on the brain 24/7.
"It's only weird if you make it weird"
Could there ever be a platonic friendship between two people who are more than friends? Friends with benefits? Friends who sleep together? Who's a better person to engage in hot, sweaty sex with than someone you already know and love so much? Although this does sound like the start to a bad romantic comedy: boy meets girl, boy and girl become friends, boy and girl casually sleep together with no strings attached, some sort of conflict arises and hilarity ensues.
Alas, this isn't a chick flick but real life. The ending will most likely be: a.) end of friendship or b.) nothing being able to remain the same or c.) all of the above.
So to reiterate the original When Harry Met Sally question - can men and women ever be JUST friends? Definitely. But there are also certain men and women, when paired together, who could never be only friends.