I would guess that about the same amount of damage is done in one hit of salvia as sitting through a 2 hour movie eating popcorn.
Your completely arbitrary 'guess' instills me with confidence. Many of these drugs have an insidious effect,
especially marijuana. Also, the conventional wisdom amongst users that marijuana is a harmless drug is wrong. There are many highly reputable scientific journal articles that are beginning confirm this. Ten years ago, there was no strong consensus in the scientific community on this issue,
but there is now. Also, there are many
rehab centres for marijuana users. Further, my friend who is a medical doctor and works in a walk in clinic says he will often see people asking him for help trying to get off of marijuana. Additionally, the whole culture surrounding marijuana use has been found rather destructive. And it's important to note that marijuana is a very different drug from what it was 30 years ago.
But I'm not interested in a debate about whether marijuana is harmful: it's a great way to derail the point, and it's a debate some users will never give up seeing as how the drug is so unreasonably glorified, which makes for a great rationalisation. Drugs are temporary, and they often do cause damage. I think a lot of the damage is often from the attitude that develops towards drugs, not necessarily from the drugs themselves. And the attitude I've been seeing is pathetic. You're never going to do anything permanently good while under the influence of drugs, or while your life becomes a search for the next high. You're never going to develop in a meaningful way. Your life will be wasted. Subjective? Yes. I suppose it won't be wasted if you are fulfilled with contributing nothing, possibly becoming damaged or dependent, and missing out on a much larger, more interesting world.