Abortion supporters explain their position by saying, "No one knows when life begins." They're lying, of course. We've known for decades that the life of each individual begins at conception. But just for argument's sake, I'll let this lie stand.
When we are in doubt, do we err on the side of life or death?
A mine shaft collapses. We are not sure if any miners survived. Do we write them off on the grounds that a rescue is expensive and dangerous? Or do we, on the chance that there may be living human beings in that mine, proceed with the rescue?
A hunter sees movement in the woods. It's probably a deer. It might be another hunter. Should he shoot anyway, since he's not sure if he'd be taking a human life or not?
A child is found floating in a pond. He may already be dead. Or CPR may save him. Do we ignore him and continue fishing, or do we try to save him?
You can probably think of a dozen examples, without even trying, of situations where we routinely err on the side of life. When there is any doubt that what we are proposing may cost human lives, we assume that there are lives at stake, and act accordingly.
Since there is doubt, shouldn't we restrain abortionists until they can prove they aren't killing children? It's the only reasonable, consistent thing to do.