Yea, the marijuana lung cancer thing is debatable, but I would think that it could cause it. You just have to think--how many people smoke weed for more than like 30 years in the same quantities as people smoke cigarettes. I have heard often that it will not cause cancer, but I am very skeptical of that. I have also heard that it does not kill brain cells, but again I am skeptical. I would not be surprised if it did not kill as many brain cells as alcohol, but it probably still does. I have never understood the whole kills brain cells thing, does that even mean anything? I thought like all cells regenerated. When people say that do they know what they are talking about? I can see it like fuck*ng up a persons natural chemical levels for a long period of time but I don't know how it would kill brain cells. Then again, I know very little about biology.
Also, I have smoked a ridiculous amount of pot as I already said and done pretty much every drug there is, but the only times I don't remember what happened are when I took oxycotin and alcohol (not together, although I did take them together, just those are the only two that caused me to forget large chunks of my life. Oh, actually xanax and alcohol did the same, but that is only when mixed.) I will be graduating college in four years with a gpa good enough to get into a decent post-grad program, so whatever that means. To be fair though, me and one other guy are the only people I know that do large amounts of drugs who haven't failed at least a semester or who will graduate in 4 years. He is actually doing it in 3 1/2, while I am doing 4 and a summer, only because I prefer taking 12 hours a semester and 6 in the summer though.
Also, again, LSD is like the safest physical drug there is. However, my friend took over 100 hits in about a years amount of time in high school and hasn't even smoked weed in the last 4 years, ut you can totally tell he took a lot of drugs. He is still really smart and has like a 3.9 gpa in a bio/pre med degree, just you can tell.
I guess what I was kind of trying to say here is that all types of people do drugs. Smart, stupid, responsible and irresponsible. It is just that the stupid and irresponsible ones get the most attention, just as in any group of people, especially ones that the government/media/large amounts of the population are against. To use a shitty example, look at reporting/general view of non-African Americans towards African Americans from slavery to the 1950's, and, to a lesser extent, today. Plus, 90% of the people who get attention because of their drug use do so because of stupid shit the did to get caught/stupid shit the tried to do not to get caught, etc., this just furthers the negative opinion towards all drug users, when it is a fairly small percentage of them (think of all the people doing drugs who don't get caught).