Perhaps this is true for most non-Christians. I believe it is possible for Christian men to be friends with Christian women without hitting on them though.
Google "married pastor having an affair"...if you are on 56k modem it might lock up your computer.
Being a Christian doesn't remove temptation. Not only is it simply wise to avoid any situation where you could be tempted, it is also smart to avoid any situation where a credible accusation could be made. Even if you would never be otherwise tempted, do you really know the other person isn't? Or do you know for a fact their SO or yours isn't going to jump to the wrong conclusion?
"I know what I am doing" -- famous last words.