What if the externality is not into the price? When the externality of it (pollution, global warming, etc) is not within the price, then yes, we do care, because you aren't paying the true cost and you transfer that cost to me.

If you have a carbon tax? Then sure. But if you dump all your emission on the rest of us and wash your hand because "you paid for it", then yes, we will question the value of a waste of energy because that's really the only thing we can do.