The American College of Physicians says its mission is to promote the “quality and effectiveness of health care,” but it’s stepped out of its lane recently with sweeping statements on gun control. And that isn’t the only recent foray into politics by medical professionals. During my term as associate dean of curriculum at the University of Pennsylvania’s medical school, I was chastised by a faculty member for not including a program on climate change in the course of study. As the Journal reported last month, such programs are spreading across medical schools nationwide.

Why...