Everything you need to know about another person you can learn in a group or non-sexual setting. one on one doesn't require isolation from everyone else. (haven't you ever had a conversation with someone at a ballgame or in a bar?)
GSA(P)
You can have a conversation with another individual within the setting of a larger group, but you may not completely get to know someone in that setting. Larger groups exhibit a stronger peer pressure influence, and this is especially true in a church group or other religious setting.
I believe that a group strong enough to limit sexual activity between its members will also constrain conversations. I want to learn all of a person's beliefs, faults, etc., independent of what their friends, parents, and other people in the church think.
Another thing is that some people are really good ``on stage'' but are not very good one on one. On the other extreme, there was one girl that I knew in the context of a group, but would barely talk to me while others were around. But when I encountered her individually, she would really open up and could talk about all kinds of things. It was only then that I learned that there was some attraction there and she was just scared that someone might notice when the others were around.