This is an old oft-debated topic, but let me quote a rhetorical question from another article to make things clearer:
"Do you see wives or husbands still chatting with their opposite-sex-best-friends after marriage through the wee hours of the night like they used to do when they were young?"
If there are such wives or husbands, they are the exception (with either extremely accommodating or cheating spouses doing the same thing), rather than the rule. Sadly for most, platonic friendships could exist, but only up till marriage with another party, after which it simply fades away or is reduced to mere "Hi! How are you? Take care. Bye!" acquaintanceship.
Many women believe or want to believe that platonic friendships with male friends can exist;
many men don't but encourage that belief in women anyway so that they could stand a chance, up to the point when the women in question marry someone else and are no longer within their reach.
So could there then truly be platonic friendship?