Graduate students are paid half time but expected to work full time and have their entire career at the mercy of individual professors. If protections will not be given freely then collective bargaining can force the issue.
Except this is still true at US schools that have had a union for many years. The pay and benefits go up a little bit but the fundamental issues remain. I've never even heard of a grad union trying to bargain for true changes in funding structure or degree requirements.
