I was a graduate student with a research assistantship position at the University of Washington in the mid 2000s, a few years after they unionized and got a contract with the UAW.

By the time I was there, even though it was only a few years after the union struggle, I didn't hear much about the union, at least in my department.

But what I knew it meant was: we had good health insurance, we had a guaranteed minimum stipend, we had the right to actually take vacation during university vacations, and a certain number of sick days. I knew from talking to oother students, that before the union contract, grad students with assistantships didn't necessarily have these things (it depended on department), and sometimes literally got no vacation or allowed sick leave at all.

I was aware of no ways that the presence of a graduate student union harmed the grad students involved -- to the contrary of some suppositions in this thread. Grad student unions exist in dozens of universities, some for years now, so it's possible to look at actual experiences, not just forecasting supposition. I was also aware of no ways the union harmed research or academics at the university (beyond of course costing them more money to treat the grad students right).

I wonder if a few years after I left, most grad students even realized what the union had won for them. The union was not very visible, once the fight for a contract was over.