It's important to keep two lines of discussion, or two moral issues, separate when we are talking about Steve Chadwick's proposed abortion law reform bill.
The first issue is the morality of abortion itself. Do you think that abortion is morally permissible, or morally impermissible?
I think that abortion is morally permissible, for reasons that I have set out at length in these posts: why I think abortion is morally permissible and follow-up posts More on abortion: the infanticide objection, More on abortion: the female foeticide issue, and More on abortion: what about disabilities?. Even aside from the morality of abortion, I think that it should be permitted, because the alternative is ghastly.
The second moral issue is the extent to which it is permissible to force other people to adhere to your own moral standards. Is it right for you to tell everyone else how they should live, what relationships they should enter into, what actions they should or should not take?
In general, in Western liberal democracies, we don't believe in the state telling people how to live. There are no laws requiring us to get married, to live in certain places, to go to particular churches. The standard response to the idea of more state restriction is to decry it as nanny-statism, or the majority imposing its will on the minority. We do have quite a few laws to co-ordinate our activities, and laws about who may access which resources, and laws about how to pay for state resources. We also have a lot of laws aimed at protecting individuals, both from the power of the state, and from each other. I don't think all of these laws are good laws by any means (for example, I think that the law around civil unions is deeply flawed), but as a work-in-progress, by and large the laws do a not too bad job of creating freedom for us. We have some laws that coerce behaviour - famously, laws that require children to be educated. I see this as freedom enhancing: it is very difficult for anyone to function effectively in contemporary society without having a basic education. But for the most part, we don't prescribe morality through our laws. Those who want the law to prescribe morality need to make a very strong case.
So... how does this apply to abortion? At first glance, the answer is obvious. My body, my understanding of the moral issue, my decision. Don't impose your morality on me.
But there's an objection to this answer. Prosaic puts it this way:
It seems necessary to point out to you that most of our laws–and all of the laws in the Crimes Act–are there to control people because we don’t trust them to make their own moral choices eg, the law against murder–do you have a similar problem with this law? If we followed your argument we would have no laws against anything and your neighbour would be free to choose to make her “own moral decision” and kill you.
She or he has got a point. If we go down the line of argument that I advocate, we end up with extreme moral relativism, where we can't make moral judgements about anything. Or even if we can make moral judgements, we can't make laws that reflect those moral judgements.
Except I think we can. We can make laws in cases where our moral judgements are backed up by reason and evidence, and the reasoning and evidence has been subject to rigorous scrutiny. The evidence stacks up, the logic stacks up, the outcomes stack up, all providing solid foundations for the law.
As it turns out, as a society we have made a strong case for prescribing morality in respect of some issues. For example, we think that rape and murder and assault and theft are wrong, and we prosecute people accordingly. There is near universal agreement on these issues. We might disagree about what constitutes rape and murder and assault and theft, but we agree that rape and murder and assault and theft are crimes. Moreover, we have strong reasons for agreeing that these are crimes, reasons to do with the wrongness of taking human being's lives, and hurting human being's bodies, and invading someone's personal space, and so on.
But there is no widespread agreement about abortion. Some people argue that abortion is wrong, but many, many more argue that it is morally permissible. Some people try to bring abortion in under the heading of murder, or wrongful killing, or some such thing, but in order to do that, they need to show that a conceptus, an embryo, or a fetus (depending on the stage of development) has exactly the same moral standing as other human beings. Giving exactly the same moral standing to a newly fertilised egg and an adult human being seems implausible at best, unless you start grasping for concepts like souls. Once you do that, you're into the territory of religion, and it's very clear that not all religions agree on the issue of abortion. So the person who wants to ban abortion on religious grounds needs to provide some compelling arguments as to why her or his religion is the correct one.
The burden of proof on those who oppose abortion is high. They need to be able to give cogent reasons for the moral impermissibility of abortion and they need to be able to show why they think that their own moral standards should be embodied in the law. If they can't make a good argument for the second issue, then in good conscience, they ought to support, or at least not oppose, Steve Chadwick's abortion law reform bill.