Can depend on the parent. Can depend on the daycare. Or could be a necessary evil. The question really should be "Why are so many kids in daycare?" or "Daycare, responsible or not?"
There is also an argument that daycare could prevent child abuse. There are some parents out there who probably shouldn't be and not having the kids around all the time preserves their sanity somewhat. If they were around all the time, who knows what could happen to those kids.
Finding a skatepark and droping them off is a cheap form of day care. Here is an app to help you find your local skatepark.
And here we have a CLASSIC example of a false dichotomy, one of the great logical fallacies. Something I learned about when I was apparently being 'abused' by parents who didn't home-school me.