DU obviously is not an accurate representation of the party as a whole. Furthermore there is nothing scientific about DU polls or any online poll. Trusting online polls is one of the biggest follies you can do.
Simple mathematics could prove this. When roughly 80% of the country is Christian, in order for non-Christians to make up a majority of Democrats, the Democrats would have to have less than 40% of the vote, and that's only if every single non-Christian voter is a Democrat, which also obviously isn't true. Duh.
But let's look at the exit poll of 2004:
http://www.cnn.com/ELECTION/2004/pages/results/states/US/P/00/epolls.0.htmlKerry got:
40% of Protestants (54% of the population)
47% of Catholics (27% of the population)
74% of Jews (3% of the population)
74% of those classified under "Other" (7% of the population)
67% of those with no religion (10% of the population)
So by multiplying these figures we can see that:
21.6% of the population are Protestants that voted for Kerry
12.69% of the population are Catholics that voted for Kerry
2.22% of the population are Jews that voted for Kerry
5.18% of the population are people that fall under "Other" that voted for Kerry
6.17% of the population are people with no religion that voted for Kerry
That's 47.86% of the population total under Kerry voters, about close to to the actual results, and of that 47.86%, 34.29% are Christian, and 41.69% are religious. So out of Kerry voters, about 71.65% are Christian, and over 87% are religious. Both overwhelming majorities.