As someone who has never smoked, I feel like this is the argument I always had with my friends who all have/do. Ultimately, their argument for smoking basically boiled down to the lack of scientific evidence that there are lasting consequences and that it was nowhere near as bad as alcohol. My argument was that there was a lack in scientific evidence, and that comparing the utility to alcohol was stupid.
It seems unlikely that a drug that affects neurotransmitters wouldn't result in tolerance, and the scientific evidence and anecdotal reports seem to confirm this. Anything that gives you a 'high' will ultimately have the opposite effect when you're sober. So in the end you'll just wind up wasting money smoking to feel normal, and you'll feel like shit when you've been sober for a while.
I did not feel like shit when cold turkey stopping a 4 year daily habit of MJ.
I know it's highly anecdotal, but I'm very thankful I spent those four years smoking cannabis instead of drinking alcohol, smoking cigarettes, or taking prescription pills.
There's a few talk on youtube where people tried to make stats of mental illness due to THC. It's not conclusive but it paints a less rosy picture than the 'natural harmless' substance one can hear everywhere.
Medicine is not a very giving topic, if you want to 'know' you better be infinitely patient and precise.
