Be careful: this is only accurate if you amend the statement to "smoking
weed is bad for you."
According to the Relman Report (the only FDA-sanctioned study done on marijuana effects), the tar content of pot is vastly higher than that of tobacco: they estimated 3 joints to be equivalent to 100 unfiltered cigarettes in this regard.
The lung-damage caused by the smoking of all that tar is the only negative effect ever scientifically-attributed to pot consumption. There have never been any demonstrated long-term negative effects through baked goods or steam inhalation through the use of a vaporiser.
That having been said, the short-term effects on memory and association are not inconsiderable. Both my personal interest in psychology and my professional involvement in computer science have pretty much forced me to forgo this otherwise delightful habit. (Students of law and medicine are strongly urged to do the same).