you know, ive been thinking about this topic. its constantly argued her and i've yet to come across an explanation that sat really well with me.
here is my newfound view. im a big fan of what i call the 10-80-10 rule. which basically means that:
10% of the people in this world are rotten to the core - utter narcissists.
80% are circumstance based. which means you can trust them provided they aren't tempted by forces that overwhelm their ability to reason or act morally. of this 80% there is a spectrum, some are easily susceptible to circumstance, and others it takes a hell of a lot (ie. one chic might cheat becuase she had an argument with you, while another might only cheat if the husband she thought had been killed in iraq suddenly is actually alive, but only has 1 hour to live nad his last wish to bang her).
10% of the people in this world are pure gold. their word is there bond. they wear their principles on their sleeves, they are honest, they would die for their family and when they tell you something or make a promise they would go through hell to keep it. these kinds of people won't cheat even if they are cheated on, they simply walk away - they see it as you broke hte contract, so its over. they take the high road.
so can women and men be friends? well the top 10% i believe can. no matter how strong the attraction, i believe they can be platonic friends and remain loyal to their spouses.
the other 90%, its playing with fire.
so as a general rule, two friends of opposite gender who are attracted to each other are likely to cross the line at some point. BUT there are exceptions to the rule and there are people who do not cross the line.
the only reason this scenario is rare is that its rare that a man in the top 10% settles down with a woman in the top 10%. so usually one of the partners is part of that other 90% and like they say, it only takes one.