Why will unionization solve the glut of PhDs? If there are already too many grad students when conditions are miserable, why will improving the conditions reduce the supply?
Grad students are not supply-limited. UChicago--and many of the other places flirting with unionization--are never going to have to worry about finding enough grad students.
Improving conditions might let them recruit better grad students, which has obvious knock-on effects for the university, even if they retain fewer of them. In general, it is not the case that one researcher yields one interchangeable unit of knowledge. We might be better off (in terms of happiness and productivity) with N calmly productive researchers than 2N miserable researchers desperately flinging stuff at the walls.
Improving conditions might let them recruit better grad students, which has obvious knock-on effects for the university, even if they retain fewer of them. In general, it is not the case that one researcher yields one interchangeable unit of knowledge. We might be better off (in terms of happiness and productivity) with N calmly productive researchers than 2N miserable researchers desperately flinging stuff at the walls.