Ok, I'll give it to you. It's possible that we get cancer from the radioactivity in tobacco. No one really knows and this is certainly a possibility. Just like getting cancer from tar is possible, it's also possible that we get cancer from a whole other source all together.
Bottom line is smoking is bad. Even if it doesn't give you cancer, it's still destructive to your lungs. Weed or not. Smoke 30 or 40 joints every day for a few years and I'm sure you'll develop a nice little hack (natures way of telling you smoke is bad).
All we can do is what seems best for ourselves based on the information that we're givin'. More info means more possibilities. Thanks for the links and welcome to the boards btw