Cotton is generally a great fabric if you sweat, because it wicks moisture and breathes. Denim started its life as workwear. However, if you're building up moisture too fast or you just get a bit wet from weather, and you have a lot of friction from walking, your thighs can get chafed to hell. I think it's odd that chafing wasn't mentioned once in the post.

I have had it happen before on a day trip in a very humid climate and it was awful. That doesn't mean I don't ever wear jeans.