The rule seems to go back to Billy Graham, but it is to avoid being alone with a woman or at an event with alcohol with women without the wife of the husband. Something like that.
For example, to put a person in another’s shoes, what if like you had a boyfriend or husband, girlfriend or wife who was taking private lessons from a fitness instructor of the opposite gender. Would you feel comfortable about this arrangement?
To me this is an occasion of sin (in Catholic thought), and maybe an unnecessary occasion of sin in some instances. You can either have a chaperone or one other person around, or just have personal training from a person of the same gender in the example I gave. Otherwise I think being alone with the opposite gender can be a scandal that gives rise to doubts, rumors, and questions.
In modern times it has become very practical for avoiding false accusations or abuse, so I’m not sure how many people don’t do something like this anyway for practical reasons.
What do you think of this rule overall?