Well, the Christian rationalization for being so up-in-arms about it is fairly easy to understand. They believe, rightly or wrongly, that abortion is tantamount to the murder of an inconvenient human, something that I think we can all agree is about as bad as it gets. From their perspective, they are saving innocent lives, which we all agree is admirable.
Asking such a person to feed, shelter, and clothe a homeless person for 18 years might be an interesting counterpoint... if you don't, they might well die (and there's certainly no shortage of people who WILL, even if you have to cross oceans to get to them), but it is indeed massively inconvenient and the insidiously handy defense of "it's not my problem," is there to save them. All in all, not a very Christian thing to say but... everybody does. Couldn't function otherwise.
As for why those in favor of abortion get worked up about it... well, it might be good to compare it to how you feel when someone calls you a murderer because you eat meat. They are calling you a horrible person because you don't follow their moral code, something that, at least from the outside, looks like it would require every bit of your effort, just to make them happy, and because you don't you're being called a murderer.
Now, imagine that a good portion of the news media/world agreed with that person rather than mostly calling their claims ludicrous. About half, or so it seems. Imagine that there were serious efforts being made to make steak illegal, and to punish those who ate meat as war criminals. Imagine if there were people not currently locked up in an insane asylum who defended vicious attacks against restaraunt owners... Can you imagine how scared you'd be?
So yeah, I can see both sides of it, and why people get worked up. One side looks at the other and sees a bunch of baby-killers, while the other look back at those who would chain them down to raising kids, alone, while they are still teenagers... and then still not be happy with them because, with their oh-so-vast experience of the world, they should have known better.
So, basically, murderers on the one side, slavers on the other. Both trying to do right, not saying they aren't... but it's a bit of a public relations nightmare.