but only in a life-and-death situation is it excusable
While I'm a big fan of Shulgin, I think this is rather stupid...
Driving under the influence of anything creates a life and death situation. Maybe in some circumstances, it's excusable - drugs worn off hours ago, medical emergency of a life threatning nature...
Regardless, in 99.9% of cases, you're only going to put yourself into more risk of death by driving.
A situation I witnessed: We need to get to the hospital. X is overdosing on GHB, his breathing is low and irregular, he's lost contact with the conscious world. Everyone else is also on a fairly high dose of G. In driving X to the hospital intoxicated, we could have killed X, someone else in the car (or all of us) another totally unrelated driver, a kid on their way to school, anyone... In hindsight: we should have called an ambulance. In medical emergencies, please call an ambulance... They'll get there faster than you'll get to the hospital (remember the road code regarding emergency vehicles) and they can provide help on the spot.
I think the biggest issue with driving scattered is patience. You get out of a rave/club in the morning, had a couple of pills the night before, it's freezing cold, you're coming down and not liking it... You just wanna get home to bed... Public transport means waiting in the cold and when scattered/coming down and working out fares for everyone. It's also gonna take longer than driving, you might need to catch a combination of trains, busses, trams, ferrys or what not to get home... Even then, they don't put you at your front door. If it's a short taxi ride, sure, most people go for it... But anything other 20 bucks, and I think people start looking for alternate routes home... Easy solution huh! Drive!
I'd really like to encourage everyone to make sure they've got a sober driver, or can get home by public transport. Sure, it's cold, you're coming down and the thought of your cosy bed is all that's on your mind... Take the time to get home safely, or you might wake up in a hospital bed... If at all.
The last thing I've got to say is think about others. You're endangering the lives of other people, which is unjust and almost bastardly.
Read the threads Pleonastic linked to. If everything that's been posted here, and those threads don't get through to you... You're not a responsible drug user, not a responsible user of the roads.
Sorry if this has all been a little harsh, but I've become quite touchy on this subject...
Be safe