Ok I will add MY OPINION to the topic. Any burning substance that you inhale into your lungs IS BAD FOR YOU! I don't care if you smoke cigars, cigarettes, pipe tobacco, stand near camp fires everyday, fight forest fires, or yes even smoke pot, any time you inhale a burning substance you WILL HARM your body. While the long term effects of marijuana isn't anywhere near the same as any of the rest, be assured it does harm your lungs. You must also remember if you smoke joints certain papers are extremely high in carcinogens and chemicals. As for the whole rat study, simply remember one very important thing, you are not injecting THC (I REALLY wish I could), the fact is you are smoking it and the effects on the body between the two are vastly different. Consuming marijuana will get you high with ABSOLUTELY ZERO waste, you just have to know what you are doing.
Now I want to address the vaporizor issue, I have been smoking pot for thirty five years. I have smoked a lot of really killer buds in that time and I have smoked out of wood pipes, metal pipes, bone pipes, ivory pipes, glass pipes, bazookas, bongs, one hitters, blunts, joints and various other smoking devices. I smoke A LOT OF POT! When I bought my vaporizor last year I had heard "you loose 40% of the THC" and the one I really like, " You will smoke more weed and you won't get as high" and my personal favorite "You are just going to waste more money on weed because you will smoke it faster." I will tell you straight out, they are ALL WRONG. The facts are: we smoke less pot because we get high faster, my smoking circle consist of very hardcore smokers, my wife and I smoked an ounce a week by ourselves, since we started using the vaporizor that same ounce last us about 11-12 days and that is sharing with our friends. We get higher (maybe a better description would be its a clearer high), we don't smell like pot when we leave, we save money, there is no second hand smoke (if one of my friends kids come walking into the room he isn't hit with the "CLOUD"), the pot taste better, and I don't cough shit up anymore. I'm not breathing in a burning substance, I'm not inhaling ANY carcinogens, I don't have to "clean my lungs" coughing up phlegm, it's not there. Don't get me wrong if you take to big of a hit on the vaporizor YOU WILL COUGH, just no garbage comes out.
Just so you know this is simply the opinion of everyone in my smoking circle and of myself. One last point there are A LOT of bad vaporizors on the market, and most of them do not work.