In defense of cross gender friendship...
I know talking about such topics may bring confusion since there are no precise definition of love and friendship and boundaries between them obey local social norms, but since I'm not writing a book and just fooling on my Facebook profile let's say friendship is jealousy free and love belongs to the sexual level.
Now let's picture a really nice guy and call him perfictio, perfictio has around 40 friends between girls and guys but is madly in love with Charitas. Now since perfictio can't be in love with 2 at the same time we can't but call other girls friends, simple hyn?
Another argument that is commonly used is that the human body behaves different from a biological point of view when around the opposite gender regardless of the nature of the connection between the two. Of course if this "change" is felt by everyone it wouldn't need to be called biological it should have been common knowledge... its not! because the effect is negligible, and let's be forgiving and say the effect is huge...Everyone gets hungry everyday... but we don't see people jumping on fast food shops stealing food... also simple innit?
Now I'm not trying to dictate how anyone should behave in his own personal life but I do wanna against the misuse of science to win shaky arguments.