None of this ever bothered any Kennedys, Pelosis, Kerrys, Bidens or other Catholic liberal politicians...They didn’t have to listen or follow the rules of the church.
So why so many Catholic Dems? Well, like every group, we have some left wing nuts. But what I see as the main reason is that Irish and Italians comprised the two largest mass immigrations in US history. They came because they were poor, and back then, the Dems were more for the working man; the Reps for the wealthy business owners who were already here.
The next generation fulfilled the American dream and followed in their parents' political footsteps. As times changed, so did the parties, but most people stuck; worse yet, some became "yellow-dogs."
That's how my Mom and Dad explained it to me, although they were conservative-minded and didn't vote their party, but their consciences, and taught me to do the same.
Now, personally, I think money is the big driver, with special interest groups soon to overtake. These people aren't even lukewarm- they have ice in their veins.