I grew up in Missouri, now live in western Oregon, have never had a house with AC in my life. When I lived in MO I definitely saw that the people who had AC suffered a lot more from the heat, the shock of going from the cold air to the outside seemed pretty bad. I also noticed that they seemed to get sick a lot in the summer and I suspect the AC had something to do with that.
If you can live without it your body will acclimate a lot better to the heat. I do want to add that I always lived in the country, the cities are a lot worse for heat, and I usually had enough sense to get the hard work done early in the morning or right at sunset, but it was the heat as much as anything that caused me to flee the midwest.
Out here it's been in the 40's at night, highs around 60 during the day, so no need for heat or AC for most of the year. December, January and February a little heat is pretty nice. I have a friend who is working on living on about $500 per month, in the winter he lives in one room of his house and just uses a little space heater, keeps him cozy. In the olden days of yore country folks would shut off most of the house in the winter and live in a few rooms around a big stove, they didn't try to heat the whole house. Some even had a small winter cabin and a big summer house, just moved back and forth Spring and Fall. They adapted their lives to the weather instead of using oil to adapt the air to them, something we're all going to have to think about.