rabbi, a chicken and milk question.

the torah says “do not cook a kid in its mother’s milk,” and the shulchan aruch (yoreh deah 87) says chicken with milk is only derabanan and fish is not forbidden at all. why did the rabbanim extend the issur to chicken? if the reason was that people would confuse it with meat, does the gezeira still hold today? and practically, is chicken with milk treated more leniently than beef with milk, like waiting less time after chicken?

bottom line, basically: is chicken with milk a fence that still does its job, or a gezeira whose reason has faded?