Unions, and the like, just move around the real problem, which is that we have too many people in academia, and that those people should move to industry.
Going in to academia is always on my mind because I would love to be on the cutting edge of research, but I can never justify leaving my job to work twice as hard and get paid 4x less.
It's a shame that you need to be rich to continue your education past a point, but it just doesn't make sense to keep going.
It is also a free market — you get paid how much you are worth.
Disclaimer: dropped out of PhD program many many years ago for this and other reasons. Don’t regret it for a second.