From Kevin Drum's post "Liberals really suck at defending abortion":
Conservatives talk endlessly about how abortion snuffs out a human life. That's the whole magilla. But if you read only among liberals, you might not even know this is an issue. We simply don't talk about it.
Why? I don't know how it polls or what effect it has on most people, but it has to be addressed if we want to win the war for public opinion. There are just too many people who care about this and need to hear simple, convincing arguments that a fetus isn't a human life in any reasonable sense of the term. We're cowards if we aren't willing to take that on.