I read about that earlier, and from a sociologiccal standpoint all I can think of is "finnnnaaaaallllyyyy".
I've been pondering this shift in public opinion and think that the 24 hour news cycle played a part. I think people are issue fatigued because they hear about it all the time and want everyone to just stfu about it. Same thing for gay marriage recently, you'll hear the most conservative people in your day to day who say they support it because they are tired of hearing about it.
I support legalization. I would hands down choose smoking weed over drinking any day of the week.