RE: Free Primary & Secondary Education - and why not free College.
Here's why college isn't free:
1 - Generally, as pointed out above, 18 year olds are adults.
2 - Also pointed out above, everyone is required to attend K-12 education.
3 - Another point that's above, public universities are absolutely funded by taxpayer dollars, so while not free, it's reduced cost for students residing in that state (with some exceptions).
4 - Not pointed out above - finally, Wadster, get to your point - HR departments absolutely do NOT screen EVERYONE for a college diploma - it depends on the position. There are some that require college diplomas, some that require college attendance, and some that need a trade school, and others that just need a HS diploma.
I hire a lot of people into my profession...let's just say it's very high tech...I've got servicemen and women who have HS diplomas (and GEDs) that work as electronics technicians and drafters. I've got a guy without any college experience at all who is my best Program Manager, as well as one with an MBA - they have different strengths, but I wouldn't trade any of them off of my team. Accountants that have a 2 year associates degree, and clerks with HS diplomas, sales guys of all types that range from HS diploma to MBA - and all work well as a team.
The point is, in my industry, I don't see HR requiring each and every employee to have a college degree; some positions do require it, others don't. And if we see an good employee who wants to go to college, or get an advanced degree - we pay for it until graduation assuming they stay with the company - the longest being an 8 year commitment. Many companies do this as well.
If I were to go back (and needed money to go to college), I would find a company that had a tuition reimbursement program and work it that way. If they see your drive and commitment, they're usually willing to invest in you - at least the good ones are.