The ideal number of jails and homeless people is zero.

Obviously you will not reach that literally. That's why it is an ideal number, not a real number. It is still a good and worthy goal.

Finnland for example has nearly eradicated homelessness. It is not literally zero but 0.08% which is pretty good.

You can also reduce the crime rate dramatically by better social security, education, easier access to mental health care and so many other things.

And don't say we can't afford these things. These measures pay dividends in building a better society for everyone. What we can't afford is having so many billionaires not paying their fair share.