I think this article is written (and this question is asked) from a very American point of view. Having grown up in another culture but spent a significant part of my life in the US, I've come to the conclusion that there's a bit too much sexual tension in this culture; as if the underlying desires are being repressed, and thus could burst out any time there's an opportunity (like, say, being friends with the opposite sex).

For me, sex and friendship are different dimensions. I can have sex with someone I'm not interested in being friends with. I can be friends with someone I'm not interesting in having sex with. My long-term relationships, of course, have always been with someone with high values in both dimensions. And I'm still very good friends with several of my exes, who have gone on to happy relationships. We stopped the sex part, but the friendship dimension stayed.