While I know the original post is from 2010, obviously lots of people are still reading so...
I'm pretty much on the side of Cybion in this. Granted, I also sort of agree with the argument that this thread is in poor taste on a harm reduction site, as was stated earlier (just because it might get people excited about driving while tripping who don't have their own private field). But, oh well, here we are:
If Cybion was in a flat field with no real obstacles I don't see how it's all that ethically different than bike riding in the country on acid (Hoffman did it!), skiing, etc. -- both of which are arguably more dangerous to non-consenting others than what he did -- not to mention IVing meth or all the other things bluelighters post about and don't take shit for. Hell, I've gone tandem paragliding after injecting 50 mg of DPT and eating a 16th of shrooms. I was in Nepal next to the Himalayas. We followed an eagle up a thermal and burst into the clouds. It was one of the times I've felt most alive. Even with the perspective of time I've never second guessed it and would do it again in a second. In a sense I consider it ethically wrong not to push one's limits.
Could I have freaked out and sent us careening into the side of a mountain? Not really. Why? Because I had bungee jumped on shrooms and tandem skydived for the first time after eating hash before it. Since then I've injected 4-AcO-DMT and gone tandem hang-gliding. I'm the kind of person who talks to cops while tripping face just to amuse myself. As long as I don't have to actually control the para-glider or the hang-glider or the parachute I'm quite confident I can trip balls and go along for what is essentially a ride (that's why bungee jumping is a good first fear test for tripping -- all you do is jump, it's all up to the rubber band around your feet). I don't mean to brag or imply I'm some fearless "super tripper." I've been shaken to my core before (and I'm quite scared of tripping and having to control an extreme experience, like mountain biking down a long rocky hill or something). I just mean to illustrate that if you want to do something "extreme" while tripping it's possible to make a rationale risk assessment, test your limits incrementally, and learn a lot about yourself as you work your way up to stuff. Like others have said, how dangerous an activity while tripping is depends on the person.
In no way will this fact ever provide rationale for endangering members of the public by doing something like driving down the Las Vegas strip with your head out the window at 90 mph, of course. That is a categorically different kind of risk that can never be "worked up to" ethically. That said, I have tripped and had my sober friends tear around corners in the boondocks and fly down hills in sports cars at 60 - 70 mph while I lean out the window. Could I have had my head sheered off by a farmer's mailbox? Yeah, but I could've had that happen sober. I was tripping, not anesthetized and totally unaware of my surroundings (adrenaline has a way of sobering you up fast) . This is the kind of driving I recommend you do tripping: as a passenger.
If you're the novelty seeking risk taking type you're gonna have to do stuff like this just to remain sane -- you risk your body because not doing it is a risk to your soul -- but it's entirely possible to get your kicks while being fairly ethical and even quasi-rational about it if you think it through thoroughly sober first (and then sleep on it, always).
