Sadly, you are correct on the babysitting front. When we moved to the four day week, most parents were not concerned about how it would impact learning, but what they were going to do with their kids on our off day. With our community being blue collar/urban, many were concerned with associated cost of finding care/taking off work, and parents of high schoolers being concerned about what trouble their kids could get into if left alone. We have enrichment opportunities on our off days, but it has been hit or miss on attendance on those days.
As a teacher, I feel very strongly that it is my job first to teach your children content and second to teach them social/emotional skills, (Should be parents #1 job, but you know..), not be their babysitter.
But...as a parent, I also get the sentiment that our society has been built on the five day week, that it is expected for children to be at school while you are at work. Not everyone has grandparents that can watch their kids on off days, and childcare cost can greatly hinder families in our community. I know my wife and I will be pumped when we don't have to pay for daycare for our two kids anymore (aka: second mortgage)