When Plato did, with all his foresight, envision the concept of platonic relationships, what was he thinking of?! My guess is, knowing as we all do about how polygamy in a sense is a secret desire of every human, male or female, he thought...."Here's a 'morally right' way to be with someone you like and not necessarily with just a single person".... Brilliant stroke of genius, some say....!!! He must have figured that polygamy would not last very long in the world, not the way society was growing towards becoming free-so-to-speak, but not so in reality!!
Why else this huge popularity of these "platonic relationships"?! Who else do you know who just came up with a type of relationship and promptly got acceptance worldwide?! (Ok ok, give or take a few years...lol)