Growing up, I saw people do stupid things under the influence of both. The # of alcohol related stupidity was of course higher, but, a friend's brother was killed while driving, and he was stoned, not drunk. I don't look at these incidents as reasons why nobody should drink, or smoke pot....I just looked at them as reasons why I shouldn't do too much, if any of either. So, I did my share of drinking to get drunk in my teens and early 20's, then stopped as it started to bore me. Also, the potheads I grew up with are so fucking useless now, it's sad. But, I also know frequent users who are insanely sharp to the point that you'd never suspect that they used. Again, these are limited observations and have informed only the way I feel about how I should go about my business, not how I feel others should. Whatever opinions I currently have on these issues are more a result of reading and listening to other people's experiences.
I really don't care what people do as long as it does not hurt others, and hopefully does not hurt themselves. Sadly, once you start getting into the realm of drugs that are not pot, you're going to end up...at the very least...hurting yourself...and I guess that's when I start paying attention again.