It strips kids of the freedom to be kids and it is completely unnecessary. When kids have to spend their free time doing homework it causes stress. Free time is actually very important in development. I think homework only contributes to the rising rate of teen depression. Also, the point of school is to learn the basics of life. If homework isn't necessary to learn it, then lose it.
Schools don't teach kids how to teach themselves (which is truly the most useful skill anyone could ever have), they just hand out worksheet after worksheet. School should be an interactive place where kids learn and grow, and if they have a good experience, when they're at home they will REMEMBER WHAT THEY LEARNED! That's how it works. That's why specialized summer camps and activities are so effective. They work without homework and still make a bigger impact.