This is because there is so much homework at school which causes unneeded stress to kids. Without school, Kids wouldn't be depressed from too much stress that they get at school. School also takes time away from kids from doing things that they enjoy. If a student likes to play sports on a team but can't make it to the practices or games because of homework, They won't be able to do something that they like to do.
Those who hate school don't even understand what school is for. School basically guides you to the world of knowledge. There are a lot of knowledge in school, And you skip them? Well you'd be having a hard time employing for a job. How is school bad for you anyways?