To those who say that the amendment is necessary to get more votes, I'd counter that voting against the bill solely because it doesn't include this amendment would be wrong. I understand that without the amendment, people would end up paying for something they feel is morally wrong; but that's the nature of democracy. I have moral qualms with the death penalty, but I wouldn't vote against a bill overhauling our judicial system just because of that.
Still, although I'm relatively pro-choice, I can understand the pro-life argument. If you consider a two-day-old embryo to be human life, then ending that life is murder. There's a long precedence that murder is a crime against society as a whole, not just against the victim; so that abortion affects you, and you have the right — the obligation, even — to outlaw it.
On the other hand, if you don't consider that embryo to be human, then it's nobody else's right to prohibit you from preventing it from becoming one by controlling your own reproductive system. It's a tough situation, and that's why it's a significant, perennial wedge issue.
But there's another wedge issue that shouldn't be one: gay marriage. Call me a crazy liberal, but it seems completely obvious to me that if we let straight couples marry, we should let gays marry, too. Unlike the case of abortion, a gay marriage doesn't affect anybody who's against it, except insofar as it makes them uncomfortable — which is not a justification to outlaw something.