In my opinion, homework is not necessary at all because students can understand material of a subject at school, not spending their leisure time at home for it. Sometimes there is so a lot of homework that students have to spend ALL their free time doing it: as consequence, they have poor social skills and no hobbies.
I think there should be homework in schools because if teachers didn't have homework, they wouldn't be able to get much done. Especially in high school when you have one semester to teach an entire topic. I remember kids would have to take it home. You would have change the entire curriculum or increase the school year in order to have no homework. Which are two big changes to the school. I can understand no homework from kindergarten to grade 6, but 7,8, and high school should have homework in my opinion. Another reason is homework could help the kids learn something with there parents if they didn't understand what there teacher said. It helps me a lot. I can understand you saying too much homework getting away from free time. I can agree, but that doesn't mean there shouldn't be any homework. Maybe a couple sheets a week and on project every other month.
Well, mostly parents are unable to help their child with homework because some subjects(algebra, geometry, chemistry) are very hard to explain for non-professionals. In that case only additional tutor can assist. However, there might be the ways when students can have no homework and still get good education and understandie all material. For example, the amount of time spent at school can be increased( I don't think that studying for extra two hours per day would too catastrophical). Also, by doing everything at school, students would be able able to ask their teachers about all hard tasks. That is undoubtly much better that sitting at home and trying to understand everything yourself for hours with no progress.