Not really a myth, you have to look at the context. If you are humping 80lbs of gear all day, conducting section attacks, generally sweating your"bag" off, then crawl into your sleeping bag in your sweaty gear, you will freeze. Especially up here in the GWN. We don't really get the chance to "chill" by the camp fire after a long day. That's why we strip down, and still practice it on Arctic Operations training. It lets the body dry out, and you sleep warmer because of it. If you have the "luxury" of extra clothes, then by all means wear them.