Unless you're part of a culture where sexual interest is assumed not to exist in the absence of fairly explicit signals, it isn't good for men and women to be friends. In fact, even if you're in a liberal culture with a strong commitment to equality, it may still be a bad idea for men and women to be friends. Cross-sex friendships, for all their supposed potential to educate people about the lives of the opposite sex, can often be fraught with peril. Left-wing strongholds like Portland, Oregon manage to mitigate much of this danger through cultural beliefs in the equality of men and women; these beliefs are often held with near-religious fervor and work tolerably well, though human sexuality is a powerful force.

  • When men and women are "friends", often, there is sexual tension present that goes unacknowledged by both parties. This sexual tension is often at the root of a great deal of temptation, which can easily break up romantic relationships if acted upon.

  • Even if people don't act on this temptation, the mere act of saying that you have a friend, especially a close friend, of the opposite sex can lead to suspicions that you're in a romantic relationship with them. This leads to awkwardness at best and accusations of cheating at worst.

  • Most sexual assault and rape occurs at the hands of acquaintances and friends, not strangers. Most men are decent people, but it's difficult to sort the decent people from the predators. This makes having male friends somewhat dangerous for women: the poisoned Skittles analogy is a good one.

  • Single-sex workplaces tend to report more happiness; when a group is mixed, there are certain topics that can't be discussed. In mixed company, everyone holds back a little bit for fear of offending people.

  • Having opposite-sex friends, especially close friends, feminizes men and masculinizes women. Personalities aren't as manly, or as womanly, in environments where it's OK for men and women to be friends.

There can be exceptions to this; the sexual-tension element is diminished when a gay man and a lesbian are friends, or when a young man and an elderly woman are friends.