Recently, I wrote about the idea emerging among some Democrats that marijuana ballot initiatives help Democratic candidates by attracting young voters who show up to support legalization and vote Democrat while they're there. The logic is similar to what Karl Rove had in mind when he encouraged anti-gay-marriage ballot initiatives in the 2004 race, as a way of juicing support among evangelicals for George W. Bush. (Rove succeeded on the latter, but is losing on the former.)
I mentioned in the original post that political scientists who have studied the gay marriage initiatives disagree over whether or not they actually helped Bush. This came as news to me--I'd assumed, as I think most people did, that they'd worked flawlessly (from Rove's point of view). The reason they were not an unalloyed good for Republicans is that the initiatives, in addition to drawing out opponents of gay marriage, also motivated supporters to show up and vote against them--and these people also generally opposed Bush. (See, for example, here.) So there was an offsetting effect.
This will not come as welcome news to the many pot supporters who were excited about my post. But it's obviously relevant to the discussion. If you accept the argument of those academics who are skeptical about the effectiveness of Rove's ploy--and their point makes intuitive sense to me--then you'd also have to believe that the effect of marijuana ballot initiatives will be more circumscribed than supporters would like to believe.