On the contrary, I think most teachers would be pretty happy if their least-motivated students left and never came back.
In some classes of 20, having the right 2-3 kids out sick can mean you cover 30% more material on a given day, and everyone has a more pleasant time, too.
The /s at the end of my message was to say that it's sarcasm. Most teachers (like most people really) have good intentions and end up being good people, or at least not bad people. On the other hand, there's always a few power-hungry people (be it in teaching, or other things) that are just here to have power over people, because that's their thing.
In some classes of 20, having the right 2-3 kids out sick can mean you cover 30% more material on a given day, and everyone has a more pleasant time, too.