Earlier quoted context omitted.
There is a whole industry of Drug War sponsored quack science that is no more legit than tobacco company sponsored "science."
There is plenty of objective, non-sponsored research that shows marijuana to have at least in some cases a negative effect. But nice work blanketing all of the research you disagree with as illegitimate.
EDIT: From last time we talked about this, some Google Scholar links--
http://www.sciencedirect.com/science/article/pii/S0890856709....
http://bjp.rcpsych.org/content/180/3/216.short
http://www.bmj.com/content/325/7374/1195.1.short
http://www.sciencedirect.com/science/article/pii/S0022395607....
Note, though, that these are pretty inconclusive as far as causality goes.