It is broader than just religion adn takes into account cultural expectations. If the community you live in is dirtpoor adn all your peers are just a poor as you, but the one thing you have in common is large families, then that very sense of community of purpose will mean that you don't give any thought to how you are going to feed the resultant kids. The community will help you becasue thats the way it is. If you are a "sophisticated Italian culturalati" that likes to enjoy the finer things of life and freedom to travel and do as you please, then kids can be a real drag. The one kid you might have may come late in life at which time you can afford to buy in as much help as you need.

The immigrant family that moves in next door however with six kids, Grandma and aunts and uncles are notgoing to be content to remain inside all day. They will play on the street, open up businesses to sell the food they like, speak their own language and not bother with yours, maybe opoen a school and then perhaps invite many of their friends to join them. Before you know it, you are a stranger in your own neighbourhood, all because of numbers. Political power must surely follow.

EDIT: We have just seen in the US election how race can affect the political process. The voter turnout of blacks was significantly increased becasue of the candidates race. This marks a very big turning point for American culture as it embraces black culture in a way which shows that it is now a mainstream force.