Teaching positions for grad students aren't predatory. They are really a form of financial assistance. In return for teaching 3 hours a week 2 hours sitting in your office with the occasional student visitor (with say 5 hours of prep work that could be done during office hours and 3 12 hour days grading exams). That's 8 hours of work a week which works out to a pretty decent hourly salary.

It's hardly luxury and when the state/university system yanks funding out during your tenure THAT is somewhat predatory but usually most departments find a way to tighten belts and make sure current students have sufficent funding.