I'd like to see some data on the increased risks of driving while under the influence of marijuana before I lump it in with alcohol but saying that ANY reduction in focus or coordination means you are a threat to other drivers doesn't seem rational as long as you are still above a minimum threshold.
I don't hate weed. Quite the contrary! But the whole point of a smoke is to put you in a different place and that place is not conducive to the safety of those around you while steering two tons of metal at 70MPH. I'll take us off on a different and probably unpopular tangent - if you say that marijuana makes absolutely no difference to your baseline judgement, reflexes, focus, etc... then you might be hitting the pipe a bit too often (i.e., massive tolerance and habituation) and it's maybe time to consider scaling back.
> cannabis half life is anywhere from 1 to 10 days. Considering caffeine's 5-6 hours and fact people usually stay away from coffee after 3PM - it's very realistic to feel cannabis for days after use.
The duration of psycho-effects is not the same thing as the half-life. The half-life of cannabinoids is not too important, as the compounds are absorbed by fatty acids and released slowly over time into the body. The actual high for a typical dose lasts a few hours; you might feel groggy for about a day, maybe two if you're an infrequent user. As for your personal experience, I know people who can function normally in conversation on weed. Personally, I can't, but other things like driving and coordination tasks are no problem for me.