According to Arthur Brooks, liberals are going extinct because the conservatives are outbreeding them. Brooks says,
Simply put, liberals have a big baby problem: They're not having enough of them, they haven't for a long time, and their pool of potential new voters is suffering as a result. According to the 2004 General Social Survey, if you picked 100 unrelated politically liberal adults at random, you would find that they had, between them, 147 children. If you picked 100 conservatives, you would find 208 kids. That's a "fertility gap" of 41%. Given that about 80% of people with an identifiable party preference grow up to vote the same way as their parents, this gap translates into lots more little Republicans than little Democrats to vote in future elections. Over the past 30 years this gap has not been below 20%–explaining, to a large extent, the current ineffectiveness of liberal youth voter campaigns today.
This fertility gap might also explain why fewer people support abortion today. Millions of little liberal babies have been killed over the past 20 years, leaving fewer pro-aborts to spew their hatred today.
It also explains why liberals are so in favor of Latino immigration. These immigrants have lots of children, are more likely to be Democrats than Republicans, and could potentially replenish the pool of liberals in America. Besides Democrats needing to replenish their voting pool, as Brooks talks about, they also need to replenish the pool of "taxpaying" workers. The liberals policy of infanticide has effectively removed 40 million babies since 1973 from growing up to become taxpayers and the U.S. population is now growing at less than one percent per year. That reduction of the working pool will increasingly put a strain on Social Security as the number of workers is diminished to pay for the aging baby boomers. Liberals hope that Latino's can fill that gap.