A lot of commenters note that political cynicism accounts for Norquist, not stupidity--as though one can't be cynical and stupid at the same time. There's a tendency to overrate the potency of calculating evil, mostly because when evil wins it hurts a lot.
That said, I think there's a strong demographic case that consistently going to the well of white resentment, indeed defining yourself as the party of white resentment, is, as a long-term strategy, politically stupid. We'll know a lot more as this decade proceeds.
In the meantime, I think it's worth saying that I don't count on diversity and multiculturalism because I think it's kind, nice or because it makes me feel all cuddly inside. I count on it because I think that's where this world is headed. I think banking on the world remaining as it was in 1968 or even 1998, isn't very smart.
I don't say this because I like rainbow huggy-time. I say this because I like math.