> Most people will just home school their kids.
Wrong and by a huge factor which is why I asked for sources. This source [1] says 3% of children in the US are home schooled. This source [2] says about 3.5%. Even you could give a source that triples those number to 10%, you are are still completely wrong about "most".
> many people on this site went through the US educational system and would cite it as not preparing them for their adult lives
How many? Not only are you speaking for other people, but this is anecdote, not evidence. So far you have a sample size of one: yourself.
> not preparing them for their adult lives
That's partially a failure on the part of parents, not schools. Schools can only do so much. Their job is basic English and math literacy along with some exposure to STEM, perhaps a foreign language and other electives. A high school education will no longer prepare you for adult life, which is why so many countries offer affordable university education. So at the best you might be able to claim that the job of public schools is to prepare you for university. Which loads of public schools in the US are capable of doing. If you work hard in most high schools you can get into a good university.
Are there underperforming schools and especially in some states? For sure. And especially in poor areas. I agree that needs to be fixed. Unfortunately that's not unique to the US.
But if all of US public education is an abject failure like you claim, then you should be able to show how much better either home schooled kids do in life (adjusting for income of parents as causation) or how much better in life kids from other countries do. Lacking either of those, then public schools are doing a pretty good job at least relatively to all available options.
I repeat again: if it were so easy to beat public schools and provide a better service, everyone would already be doing it. It's not that easy. Just as one example, after accounting for the socioeconomic background of students, public school students scored higher than their private school peers on a federal math test [3]. Abject failure?
[1] https://nces.ed.gov/NAAL/lit_history.asp
[2] https://www2.ed.gov/about/offices/list/oii/nonpublic/statist...
[3] http://www.nea.org/home/17824.htm