It partly depends on how much you want to rough it. But where you camp is, I think, the biggest issue.
In higher elevations, it almost always cools off at night. Personally I would never consider AC. If the camper I just bought had come with AC, I would have removed it. But I'm in Montana. All my camping is here and the surrounding states and the desert. The southeast? I'm not sure you could make it...
The coast is probably not bad either. The desert is great. All those places regularly fluctuate 20-40 degrees between night and day temps. Just wait till the sun goes down and open up the windows. You can typically find good shade during the day, too.
I would guess it's different in the midwest and the southeast.
But so much depends on just what you're willing to deal with. It's totally possible to do without. I've never let my heater run through the night. But I've camped when it got into the low teens (F) at night, with just a big down comforter. But I DO turn the heat on in the morning. But back in college, I'd go down to southern Utah in January sometimes, and tent camp. 50's and sunny during the day, 20s at night. No problem.
So...a lot just depends on what you're willing to put up with. I mean people survived all this time, up until very recently, without AC. But then we don't have campers so that we'll suffer...we have them to be comfortable. But everyone has a different idea of how comfortable they want to be.
So yeah, it's completely possible.
I agree with the post above me, but also believe that people are unnecessarily comfortable these days, if that's possible. I mean people in Montana DO have AC. Some people. Some people feel it's necessary to always be climate controlled to a "comfortable" temperature. Other people just deal with the local conditions.
Which type of person you are determines whether you want AC, as much as where you happen to live.
I would personally rather sweat in bed at night than feel that cold, artificial air AC creates. But that's just me