Anti-abortionists don't believe that life begins at conception.

[Husar]

It is easy when you consider how infinitely replacable we are and how often nature (or god if you're so inclined, the blame can go either way) kills us at the slightest provocation.

Not to mention that bringing a child into the world when it is unwanted by it's parent is one of the worst fates you could inflict upon both parent and child.

The world has enough orphans and broken homes without forcing parenthood on the unready and unwilling just to soothe unaffected consciences.

But if you take all of that, we might as well euthanize orphans to relieve them of the horrible mental pain they must be in.
And I'm not sure whether all the bad parents actually go for abortions, in many cases it may be parents who just worry too much and would be really good parents once they have the baby. And then there are probably babies which are never born due to pure financial/convenience reasons. I can somehow see abortions being okay relatively early on, while the lump of cells thing is still relatively valid, but especially late abortions seem unnecessary unless there are serious medical complications.