Why is homework manditory?

In order to define homework, i decided i would have to find out why we have homework. Homework is meant for us to practice and retain what we have learned in school...

I will admit that if one does their homework it does help them to learn, but a lot of people are already smart enough to learn the material taught in class without doing homework. For example, let's say a math teacher teaches a class how to use the quadratic equation. Half of the class understands the lecture and half doesn't, but they BOTH are required to do forty questions for homework! The half that already understands the question without having to do them will spend at least an hour doing unproductive work. No what about the half that doesn't understand?

I'm sure that almost everyone has copied homework either because they didn't understand it or because they just didn't want to. A lot of the time the people that don't understand the homework will copy the work of a student that does know how to do it or will make up some work so they can receive a completion grade. The smarter students are being punished with homework that they already understand while the students that need help are copying. So what should we do about this?

Homework should NOT NOT NOT be manditory because it can be very repetitive. Most kids either half ass, don't do, or copy their homework for a completion grade anyways. (in the case of academy AP history, ALL homework was a completion grade which in a way encouraged us to not try our hardest) So why should a large portion of our grade be based on homework? Teachers don't like spending time after school to grade it and i know that students loathe doing it. It's a lose lose situation for everyone and thousands of trees are cut down and made in to paper for homework.

Homework: A manditory ineffective environment destroying attempt to get students to retain information.