I think this is a good idea. I also don't see a slippery slope. An abortion is different from losing your baby/feotus in an attack.
Personally, for me life begins at conception.
These kinds of laws have already been passed in the United States, and there have been many lawsuits filed in order to use this as the basis of making abortion illegal. Usually the lawsuits are found invalid and thrown out or not held up by any judge, but they are still filed.
It doesn't seem like a slippery slope, but the intent of the people making this law isn't to protect babies, its to erode personal rights. That's the problem.
The only thing this kind of law does is it allows a court of law to file double murder charges against someone who murders a female who is pregnant, regardless of intent or knowledge of pregnancy. I'm not sure what purpose the law will have when the murderer is already going to be found guilty for murdering the mother.
There are, however, circumstances in US law where we've found this kind of law is found to be greatly abused. Many times babies that are stillborn can have a claim that the baby was killed, and there are circumstances where the US law has been used for revenge purposes. Example: Male boyfriend is hated and disliked, and mother has a stillborn baby. She accuses the boyfriend she hates for abusing her and killing the child.
All said mother has to do is create a few bruise marks, take a few photos, and use it as evidence in a court of law. It becomes a he said, she said argument.
The father, who may not have even been living with the mother, could be found guilty of murder when he did nothing.
It makes murder more of a he said/she said argument and open up a whole can of worms.
The intent and purpose of these kinds of laws aren't very clear. The end result is many times worse than what happened before the law passed.
My rule of thumb is that in Canada there is not a huge nationwide problem of babies being murdered, therefore this law is totally unnecessary and the legal waste and new tangled rules it creates is totally unnecessary.
You are risking more lives in the legal system by creating a series of he said/she said domestic arguments for people who hate each other than you are actually attempting to save lives.
If you end up with more people in prison who are not criminal people, and you in the end save no babies, what is the purpose of this law?
The purpose might be to rouse support among right wing religious types and pro-lifers who are sensitive to this topic and might otherwise not support your political party, but feel obligated to due to this emotional law.
Its all political in the end.