I do believe in Star Trek education is free, and I do believe that students are encouraged to follow their dreams, but here's the thing.
Everybody I know who has a good job once had a terrible job. They once lived off crappy wages where they could barely make ends meet. Everybody I know who was unwilling to take any job that wasn't exactly what their education prepared them for lives with their parents.
There's no reason to think things are any different in the future. You start out doing the crappy jobs nobody else to do, then you prove you're a hard worker and get a better job later.
So just like modern day, people who get out of school and expect to immediately get their dream job are always disappointed.