On the topic of jeans, I've been wearing denim trousers & cotton shirts for the last 30 + years & never had a problem with them, but then I do wear waterproofs if it's raining & gaiters if the vegetation is long & wet. I don't wear clothes in a sleeping bag so no worries about getting chilled with damp clothing. I don't doubt that wearing heavy cotton clothing in the hills may lead to hyperthermia should the wearer get wet but it's more a problem of walkers being unprepared for weather changes when setting out, Common sense has more bearing on the matter than the type of fabric your trousers are made from.