Empirical evidence seems to indicate that marijuana improves my creative problem solving capabilities substantially. Then again, it can hinder the normal solution methods at times too. For example, I once struggled for about 10 minutes to compute 3 * 0.25 (definitely an exception, it usually does not impair numeracy so severely), but I approached the problem in ways I had never imagined before. A supposed 4-point temporary drop seems well worth the longterm effects of remodeling my perspective on, well, everything. I think I owe a lot of my intellectual development to that wonderful plant.
If society is open to allowing psychoactives with demonstrably negative long and short-term effects (i.e. ethanol), then why not allow psychoactives that make me creative, philosophical, non-belligerent, and in general the happiest man alive? One of my favourite inside jokes when high is to think that "Feeling this good should be a crime. Oh wait, it is" It's quite a depressing thought that it is in fact illegal to ingest (who inhales anyway? there are far more effective ways to go about it!) something to make oneself happy while not infringing on the rights of others. Unfortunately, by disobeying the law in this matter I am risking all credibility in my profession due to the strong social stigma against it. It's too bad that people fear that which they do not understand, that which they have only been told bad things about growing up and are thus nearly unable to form their own informed opinions on. However, as a greater portion of the population practices such peaceful civil disobedience, it drives the eventual rescindment of marijuana's illegality (at least one can hope).
I have been surprised to learn how prevalent this form of civil disobedience is. Perhaps a lot of people conceal their use out of fear (it's illegal, and socially frowned upon) as I do. Perhaps there are more benevolent marijuana missionaries out there spreading the word of peace and happiness.
These papers studying cannabis as a risk factor for steatosis and hepatitis C (a finding which is contradicted by another study that I can't find at the moment) indicate that 24-30% of patients use it daily (in France at least, but I've seen similar numbers for other locales).
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WFX-4R7J81G-5&_user=10&_coverDate=02%2F29%2F2008&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1212900528&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=fb8c342ecca065efc61e77e527067e0f
http://www3.interscience.wiley.com/journal/110493927/abstract?CRETRY=1&SRETRY=0
If that proportion ever exceeds 50% or so, I see no alternative for governments but to concede to the will of the people and legislate accordingly.