Certainly, the No on 8 folks might have done a better job of outreach to California's black and Latino communities. But the notion that Prop 8 passed because of the Obama turnout surge is silly. Exit polls suggest that first-time voters -- the vast majority of whom were driven to turn out by Obama (he won 83 percent [!] of their votes) -- voted against Prop 8 by a 62-38 margin. More experienced voters voted for the measure 56-44, however, providing for its passage.
Now, it's true that if new voters had voted against Prop 8 at the same rates that they voted for Obama, the measure probably would have failed. But that does not mean that the new voters were harmful on balance -- they were helpful on balance. If California's electorate had been the same as it was in 2004, Prop 8 would have passed by a wider margin.