Ah. Well in that case I missed your point somewhat, so thanks for clarifying. Still, I would like to point out (somewhat cheerfully) that the case is self-limiting. It can be observed in the more radical example of African Americans, among whom the percentage of births to single mothers is a staggering 77%. The result is that African Americans have no capacity to out-compete other groups and are therefore only a 'threat' insofar as they are able to render certain areas uninhabitable to those groups.
So, I would emphasize that for people such as you and I, the challenge represented by those who follow the lifestyle you are describing is that they are pretty crappy to be around, but they do not represent any real threat to life and limb. I realize you aren't trying to make that point, but I think it's worth keeping in perspective.
In short: the Left cannot create, only destroy. Destruction is often unfortunate but always limited to that which has been created.