Lots of studies find that too much homework (3 or more hours) makes it worse, but a study that tracked 3,000 students over 15 years and found that more than 2 hours a night of homework is linked to achieving better results in maths, English, and science. A 2009 anonymous study showed that kids feel angry and less confident when homework is incomplete, which leads me to my next assertion. When homework is complete students feels a sense of achievement and can feel good that they completed a hard task.
Yes, students may have a sense of achievement when homework is completed, but that doesn't mean they won't feel burned out and uninterested. School is supposed to provide a broad, basic education, not a specialized one. But with after school homework, kids don't want to pursue a more specialized education, they want to spend every spare minute socializing, leaving them unprepared for getting a job and choosing a career. On top of that, just because completing homework gives students a sense of achievement doesn't mean they aren't going to get frustrated, annoyed, or uninterested and blow it off, or do mediocre work and not make any progress.