I've always been iffy on the issue of abortion because this issue requires us to define what is a life that matters to us.
Clearly, human life cannot be enough if abortion is considered correct, since the fetuses are human. But what do the fetuses lack that most other humans have?
I think the difference is in two things: Sentience and nervous system. If a fetus has developed either of these two things, I would consider it morally wrong to abort such a fetus. Here's why:
If a fetus is sentient, then it is aware of what is happening to him and in this respect is as worthy as a small child.
If a fetus has developed a nervous sytem (but perhaps is not sentient), then the fetus feels pain, and even if this pain cannot be interpreted by the fetus, it is still pain that we're causing to a human.
Hence, the time limit matters, and it should be set accordingly to what science can tell us about the development of a nervous system or of sentience.
For example, if either of these things were developed 1 week after pregnancy, then it would be morally wrong to abort after that. If, on the other hand, they were developed on the 30th week of pregnancy, then at that point it would be immoral. Right now I honestly have no idea at what point these things develop, but if they develop at around the 20th week, then I consider that part of the bill to be correct.