All depends on how big the tear is, and how much of your insulation is from the pants. A draft in town in good weather might be embarrasing, but in the woods in really cold weather, it might be the equivelent of stucking ice in your pocket. And there are some nice big blood vessels that are full of warmth there. And frost bite to the inside of your thigh or to the urinary tract just sounds so bad.

Your clothing is part of a hostile enviroment suit. Not a space suit, besides, space kills you pretty quickly and gets it over with. Space is nice that way. Cold air, cold air is evil.