Then you went to a bad public school.

The way you say this implies that there's some easy way to move your kids from a bad public school to a good public school. This is of course laughably wrong, since moving schools requires buying a home in a nicer/more expensive area.

If you’re sending 3 kids to private school for $1000/month each, you could afford instead another $400k of mortgage or so on top of what your mortgage already is with todays interest rates.

That’s almost as much as the median home in America. So assuming you already live in the median home, you could send your kids to private school, or you could buy a house that’s twice as expensive.

Where I grew up, the median home is less than the national median, and the public schools are pretty good.

No, I went to three bad public schools.

And people I know went to many bad public schools.

I on the other hand went to public school and would send my children to one. Anecdotally, some of the most successful people I know went to public school, many of which had parents that could easily afford to send them to private school.