I'm going to disagree with the "cotton kills" theory. Not to suggest people discard synthetics and go back to cotton, but to illustrate a concept I'll call "Living within the limitations of your gear."
I grew up with cotton and didn't use synthetics until the middle of the season last year. One of the things I emphasized with my son was staying dry. At the time, it was one of the most important paradigms for being in the wilderness. We planned our mileage early in the day before the rain which is quite predictable in Colorado. If it looked like an unexpected storm was coming, we made camp early and sat in the tent. We usually don't have all day storms here.
The military had cotton fatigues until sometime in the 80's. We learned to deal with them just fine, so it is possible.
The second concept is "Recognizing a problem before it becomes a problem." The problem OM described wasn't just cotton. It was combining cotton with a soggy trail. It's pretty impossible to tell a teenager not to get wet. But a simple solution would have been to wear rainpants and go a little slower if needed so the jeans didn't get wet from the inside.
Cotton has advantages on the hot end if it's lightweight. It is much cooler than synthetics and it doesn't smell as bad. In colder weather, I'll wear the jeans. I gave up the car last October to May and road hiked almost everyday regardless of the weather. Jeans are warmer in cold weather and a lot tougher than flimsy synthetic pants. You just have to recognize the limitation and put on rainpants if they are going to get wet.
I'm going back to cotton. Light cargo pants and a cotton shirt with a pocket for my camera. I seriously doubt I'll have any problems. There are a couple fallback positions. If my pants get wet, I can just wear my rainpants. If my shirt gets wet, I can take it off. It won't make much difference in warmth if I put my fleece and other layers on over my skin. Worst case, I can set up the tent and get in the sleeping bag.