All his "conclusions" aren't particularly insightful:
-Smoking harms your lungs
-External agents that have a strong effect on the brain are bad for developing brains.
-Mental state altering drugs can empower or trigger existing mental health conditions
-People who use mental state altering drugs continuously might experience negative affects in their social and professional life.
The same could of course be said of alcohol, caffeine, nicotine, a large number of non-prescription drugs and virtually all other drugs that affect your brain in any way. (switch a few organs around of course)
Of course this is all true, but it's a calculated risk you should be allowed to take based on all the incredibly positive uses Marijuana has. This is were personal choice comes into play.
Also the writer of this article:
"I'm a conservative Republican, have been all my adult life. I volunteered for the Reagan campaign in 1980. I've attended every Republican convention since 1988. I was president of the Federalist Society chapter at my law school, worked on the editorial page of The Wall Street Journal and wrote speeches for President Bush—not the "Read My Lips" Bush, the "Axis of Evil" Bush. I served on the Giuliani campaign in 2008 and voted for John McCain in November. I supported the Iraq War and (although I feel kind of silly about it in retrospect) the impeachment of Bill Clinton. I could go on, but you get the idea."
He's a politician who is looking at this issue from a very narrow perspective.