One argument in favour of legalization I've heard fairly frequently is that recreational cannabis use is also medicinal, insomuch that it reduces stress and anxiety, lowers blood pressure, et cetera. The argument is thus: if cannabis has medicinal benefits, who is to say whether one's "recreational" use of cannabis (as part of a personal health regimen much like seniors take Aspirin daily) is less valid than how a cancer or AIDS patient uses it, and further, because the line between recreational and medicinal use is so blurry from this standpoint, recreational use should be allowed vis-à-vis full legalization.
I should back that statement up a bit. Clearly, a cancer or AIDS patient has a greater need for medicinal cannabis than a recreational user; this is not the argument, these people would clearly be much worse off without cannabis. What's being argued (Albeit less-so in, say, California) is the validity of the assertion that cannabis should be reserved for cases with critical needs, almost as a "last ditch effort" to help people suffering from the worst illnesses known to humanity.
Recently, the guy who runs WeedMaps.com got some flack from the medicinal community when he was interviewed by media and made light of California's lax requirements for medicinal cannabis. The danger of the "recreational as medicinal" approach is that the medicinal lobby has fought tooth and nail for credibility over decades of heartache, and with more and more states opting to allow at least limited medicinal cannabis usage, the last thing needed is for more conservative states to see the medicinal lobby as a Trojan Horse for full-on legalization. This is also part of why many in the medicinal community are against legalization; the U.S. federal government doesn't even acknowledge cannabis has medicinal benefit yet, much less be on board for letting everyone in the country smoke it.