I'm sorry that anyone is ever killed by an impaired driver. We have laws against that. But in this case it could just have easily been a drunk driver, someone on an over the counter cold med, someone with a sleeping disorder...the list of things that impair drivers who then have an accident is long. There was a story here this weekend about a kid text messaging who hit and killed a guy on a bicycle.
From the research I've done, it's far more benign than drinking in every way. Anecdotally, I've known several regular users, but unless they told you, you'd never know. It was for them what having a cold beer or two after work was for another. There are better, more productive ways to relax, but let people decide that one for themselves.
I have know many people who lost their lives due to drinking, either theirs or someone else's. I've seen more than a few alcohol fueled fights and craziness. Pot doesn't seem to make people as aggressive nor as stupid as alcohol. But I'm not for making it illegal again. We tried that and it doesn't work. Doesn't seem to be working with marijuana either.