Culture in departments is rooted in history; by analyzing the historic culture of physics departments, we can better understand attitudes, assumptions, and ideas that permeate contemporary culture. We examine the evolution of the idea that physics education should serve as a filter, a practice commonly called gatekeeping. Physics graduate education saw great reform throughout the 20th century that developed many of the structures that are present today. In the present, our field is more diverse than ever before, and our current standards and expectations fail to support these learners. However, this failure is seen as the student's failure rather than the system's failure. This project analyzes arguments for and against calls to expand the field through 20th-century primary sources using a concept from social dominance theory called legitimizing myths and advocates for a reconsideration of the values that justify many of the arguments for the continuation of inequitable practices.