From friends to lovers

Recently, my attention was called to a message in a polyamory forum about turbulence in a polyamorous relationship caused when one person wanted to start dating a friend, and that person’s existing partner wanted to impose a “No dating existing friends” rule.

I haven’t seen many examples, at least so far, of people prohibiting other people from beginning romantic relationships with anyone who was already a friend. Yet as I read this message, it seemed many other people on that forum had, or wanted, similar rules.