University professors are part of a self-screened, self-regulated profession who owe their careers to the existence of a cartel maintained by federal and state laws governing the accreditation of colleges and universities. This is a crucial barrier to entry. They are rent-seekers in a closed profession that screens out conservatives, beginning in the freshman year in college, and has ever since 1948. I recommend this milestone: Economics, by Paul Samuelson, first edition (1948).