Your reasoning is correct, if and only if adjunct professor positions are filled as intended. The article mentions that adjunct professors make up over 50 percent of faculty at various colleges and universities. If it is so -- I am not qualified to evaluate -- then your argument falls at the base.

If adjunct professors are over 50 percent of faculty, then the position is being used by universities to hire cheap. This leads to obvious problems for professors but, ironically, in time kills higher education. Higher education requires individuals who are free from the worry of making ends meet, so they can pursue knowledge. They need not be rich, but they can't be counting pennies. In time, a staff made up of strapped professors hurts the teaching quality, destroys the perception of quality at universities and scares students away.