All of us have that one friend: the one that understands you a little more than everyone else, the one that gives you a different perspective on things, the one that nobody stops bugging you about. A friend of the opposite gender isn't unlawful, but it seems like society has found ways to shun it. No matter what the scenario, no matter how different you think your situation is from the others, a guy and a girl can no longer just be friends without the worry of societal defamation.
It seems like too many things can go wrong. In the case of a man, for example, having a friend that's a girl holds you accountable for your own feelings, which is not something most men like to worry about. The risk is unfair, and the slightest indication of even a crush jeopardizes the relationship as a whole! Yes, it can be argued that this goes for both men and women, but the social expectation of a man to make the first move forces him to make an initial decision: go after her as more than a friend or set his emotions aside and work for the friendship, promising himself to keep those emotions in his back pocket.
On the other side of the spectrum, a woman would have to worry about her reputation, continuously evading the "ships," from her friends. There is no inter-gendered association that escapes the constant murmurs of "Oh they should date" or "You two would look SO good together." This societal influence becomes a reason for the two friends to overthink their relationship, and it fundamentally complicates everything. A true friendship would obviously hold its ground, but the awkwardness makes it harder for both parties to be friends on a personal level.
And then the romance side takes its toll. What happens when one of you starts dating? Jealousy is obviously an immature trait, but it's built into the human brain's system! If a guy and a girl take the risk and become friends, then it is obviously gratifying to see one or both of them dating, but what happens to the significant other? He/She is now dumped in the middle of a friendship and may feel threatened by the closeness of two people of the opposite gender. It only takes one of these friends to put their love life first and forget the relationship that they've built.
Nonetheless, that's the risk, and this is how society has blocked off anything more than a familiarity between one girl and one guy. A guy and a girl cannot be "just friends" without complications.
Don't get me wrong, having a best friend of the opposite gender is an unbelievable experience that gives you so many different outlooks on how things work. From the constant fights my best friend and I get into about "which gender has it harder," to the deep talks we have about the perspective of both genders, it's a blessing to be her friend, but it does come with a price.
Today, a guy and a girl cannot be just friends unless they're willing to sit through daily conversations with their group blabbering about their ship name, unless they're willing to set aside their emotions, and unless they're willing to stay persistently dedicated to the friendship itself. Somehow, society has found a way to break apart another method of self-expression, and this one really holds back what could become exemplary friendships.