It's interesting. I completely side with the anti-singleton argument from a theory standpoint, and yet my cube remains singleton. As far as I'm concerned, cube is a custom collection of cards. Period. The resistance of some people to playing multiples is hypocrisy at it's highest level, especially when those same people run functional reprints. The lack of critical thinking on that baffles me to no end.
With that said, there are two small objections I personally have with running multiples (functional reprints or otherwise). These have held me back from running multiples:
1. Variety. If I'm doubling up on cards, I'm reducing the number of unique effects in my cube. If we are talking just a handful of cards, it probably doesn't matter. But at some point, I'm making fewer viable decks, not more. And that is against what I want to do in cube.
2. Limited vs Constructed. The more we double up on cards, the more drafted decks will start to resemble constructed decks vs limited. There is nothing wrong with that actually. But I personally don't want that because I dislike constructed magic. I don't like the consistency and the polarizing effect it has (from an archtype A beats B beats C beats A standpoint). I like the fact that in cube you build a deck and no matter how consistent you try to make it, each game plays differently because the reality is you have 24 unique cards in your deck. You don't have 4 copies of 6 cards (where every draw plays more or less the same).
Again, I think exploring multiples of key cards that make certain decks work is a solid approach. I've held back due to the above, but the more I read here and look at different cubes, the more tempted I am to try running a few multiples (gravecrawler in particular).
