I think men and women can be friends. If they are both clear what they want from relationship and clear about rules of their relationship it is possible. If men and women can work together, sure they can be friends too.
One person would usually have more attraction power in such relationship, whether it's man or a woman. They could be attracted to each other, but as long as they follow acceptable friendship guidelines, they would be fine.
Men are more visual and could be more sexually attracted to a woman friend though. Women can be attracted to a male friend too but woman's attraction is more complicated and rare in this case.
Sometimes, very religious people avoid such friendships because there is "too much" temptation in their opinion. Some of them are affraid even to look at the opposite sex since sinful thoughts come to the mind a lot. It is usually men who suffer from it. As a woman myself, thoughts about sex aren't coming to my mind when I look at someone. Women need to be attracted emotionally first for them to be tempted just by looking.
If you don't suffer from temptation or don't have strict religious views or restrictions, then why not to be friends with the opposite sex? Aren't we all should love and take of one another?
Some men would find it very frustrating to be "just friend" to a female who he finds very attractive. He would never feel comfortable in such friendship, so he could decide to leave. It's much easier to be friends with someone who you don't find attractive.
Sometimes man and a woman try to be friends at the beginning but then they discover they want each other more than friends and one of them quits or back off. Sometimes man and a woman are attracted to each other and then become great friends.
A great foundation for friendship would be if man and a woman don't find each other very attractive but have something common to talk about or have common friends. If one or the other is more attracted, then it could lead to the power imbalance in the relationship and future break up.