No, the guy is just misinformed. You won't become unconscious at 12500ft. In fact it's perfectly legal to fly at 12000ft for 30 mins. Pikes Peak is 14115ft and I don't think people are all becoming unconscious up there. Also there will always be a very obvious alarm sounding when there is a depressurization. In the Helios flight they just thought the warning was something else (i.e. pilot error / incompetence).