If I had made a bundle in the dot com bubble or something, I could see myself teaching CS in CPS. Or at least trying -- I teach grad school and don't know if I have the personality for younger students.
Then you illustrate my point exactly. If you were already independently wealthy you would do it. But would you have chosen that career path straight out of college or after a few years in industry?
Also $75K isn't much if you want to live in Chicago, home of the 12%+ sales tax. I recently lived in Chicago and as a single guy I could be pretty comfortable on $75K but I wouldn't want to support a family on that. If $75K is the average then thats probably for a teacher with 10+ years of experience and some advanced education. You are not going to draw away talent from the private sector or draw talented graduates out of university for a starting salary below $50K in a high cost of living area. The teachers union won't allow you to pay talented professionals more than a teacher with more years in the district, so someone out of industry will start in the bottom range of salary.
They feel good, blah blah blah, ect... I knew several people who did Teach for America and I know 2 teachers who left CPS, one for a suburban district and the other to go back to school. Teaching in CPS and other inner city public and charter schools sucks. Its exhausting, thankless, low paying, and sometimes dangerous. You might think you are "changing the world, making a difference, impacting someone's life", but you aren't and that has a huge affect on young teachers moral when they realize it. You are babysitting the students, you will have no professional support, no supplies, no budget, and some really old and outdated books. You might be lucky if your students are only a few years behind the curriculum of the actual grade they are in. Fuck that.