I've never understood the "it's natural so it must be better for you" argument. It being natural just means that it wasn't made to be used by the human body. If it's made in a lab, that means it was tailor made and created for human beings by professionals who know what they're doing, rather than random chance.
You changed your post. Yeah, theoretically chemists could add lethal stuff to their drugs. But literally what reason would they have to do that? They'd kill off their customers, ruin their reputation, and make a lot of very powerful and dangerous people angry. Sounds like the worst idea around. Also, you definitely can't see "what's in" weed. Let's use 2C-B as an example. A five milligram dose, smoked, will get you high. Five milligrams of powder, for the record, is about ten grains of sand. You could easily hide that inside weed, especially dissolved in water.
