A big thing public education does and was created for was to lift the floor of the knowledge level of the masses. We all have at least a similar-enough foundation of learning and knowledge to really interact with each other. No longer do you have these pockets of 'others' that might as well be a different species, due to their world view being so completely different than the rest of us. We receive at least a rudimentary level of knowledge to allow everyone to read, write their thoughts out in a manner that can be understood, and number computation to work problems out for ourselves. That's a big deal.
I don't think people realize what the ramifications of only educating those in privileged positions and even those who seek it out would look like.
It's not really helpful to anyone if an entire legion of our populace doesn't know jack shit.
A great mechanic might not need these skills to be a great mechanic, but it's nice that he can read a note left from a fellow mechanic about a car, write a note for a fellow mechanic or the customer, and maybe tabulate multiple costs and a tax to the bill. These are things we take for granted now, and it's because of the Dept of Education.
Now obviously, there's a ton more nuanced, complicated, and tactful aspects to it all that matter and come into play here, but from its origins, that's the most basic one.
If we keep leaving important entities like the DOE to the states (you know, The States of America, not the United States of America), the gaps that already exist like between the people of Mississippi and New England are going to explode. And over time, certain areas of our country will become what Trump might call "shithole states."
