If people are religious minded, then why would they want to be any kind of friend with a member of the opposite sex if it is not for any purpose such as work or something else purposeful?
The hadith, "When there is a (non-mahram) male and female alone together in a room, the third person is the Shaitaan."
This is probably why I believe that a boy and a girl can never just b friends.
True, the interaction is only allowed when a person is working in a place where the interaction takes place because of the nature of the job, without discussing anything other than business.