Of course first grade teachers and working parents like it, it's free daycare and makes the teachers jobs easier. That doesn't make it an utter necessity. Half way through first grade they are all doing about the same either way. I thought offering it as an option was a great idea and was ticked off when they took away the option part and I had no choice but to send my youngest all day.
We pump more money into schools than ever before, we start kids younger, and keep them there longer. We are even talking about taking away summer vacation and making them go all year long. Yet somehow, none of it is making things "better." We always hear about how our system is "failing" our children. Maybe it's because what they need to learn cannot come from a classroom. Letting kids be home, unscheduled, running around the neighborhood, interacting without constant adult supervision, making friends, solving their own problems, hanging with mom and dad or grandma and grandpa while learning from them, free time, free thinking... that's what kids don't get anymore.
I'm as guilty of this as anyone. My kids are so scheduled, it's crazy! Not everything about "the good old days" is better than what our kids have, but this part is. No amount of money or hours in the classroom can duplicate it.

With me
Loved teaching them to read. Loved teaching them their math skills. Loved going to museums and science centers and nature walks. Loved them being with me
Although, that still means nothing. My best friend's son couldn't tie his shoes until second grade and is now a pediatric neurologist. I am sure his kindergarten teacher is still tsking her tounge over him not being able to tie his shoes, but life is ok for him now
I was a stay at home mom the whole time. My 2nd dd walked at 9.5 months.. after that I lost track of who walked when. 
He grad. from K this year. I know k changed between when I went in 81 (half day) to when my brother went in 84 (full day) I'm really surprised there are still places where its still half day! My 2 yr old will be going as an almost 5 yr old to prek which should make things easier on us. He's very excited to go he has his own backpack he wears to the bus stop each morning I on the other hand can wait a few more years! 