I think the problem is - all of us here (on bubhub I mean) are perfectly capable of reading to and doing educational activities with our kids, and in fact have been doing so since they were babies. Our kids aren't really the ones that homework is targeted at.
There are parents out there who have no interest in their child's education, don't bother reading to their kids, have never even introduced their kid to a book or a newspaper... These kids are already at a huge disadvantage compared to our kids, and I think compulsory homework is aimed at trying to help them a bit. If homework was optional, do you think these kids would do it? No way. Our kids would do it, but it's not our kids who need it. So what would be the point?