Christopher Yuan suggests that when we get asked by pro-abortionists “How many children have you fostered/adopted”, we should respond with the question “how many babies have you murdered,”

It sounds at first like a witty retort to what has been seen as a witty retort to the pro-life argument. However, I think it ultimately fails. You see, the pro-abortionist does not accept our premise. First, they don’t believe that abortion is murder, secondly, they do not consider themselves culpable.
Now personally, I could simply respond to the original question factually. We have adopted. I could also point to the work here in the UK of Christian charities like Home for Good, Safer Families for Children and in terms of wider childhood welfare, we might add in Christians Against Poverty and TLG. I might add further that many of the adoption agencies have Christian roots.
However, I think the question treated simplistically may be a bit of a red herring. You see, first of all, it is rare that abortion was on the table for families where adoption or fostering is being considered. Birth parents who have their children taken into care don’t tend to be considering the possibility of abortion. In fact, the child may have gone into care against the birth parent’s preferred wishes though they may come to recognise that this is in their children’s best interests. This means that I would also not be too concerned if you are unable to say that you have fostered or adopted.
The question I really want to respond with is “Do you consider abortion, all things being equal, to be a good or a bad thing?” Whilst some people may respond by saying that yes, it is a right and a positive right, I suspect that is rare. Many people support abortion as a necessary evil, partly a consequence of the belief that the mother’s bodily autonomy should trump all other ethical concerns, partly because they see abortion as necessary to save lives and in contexts where there has been rape and abuse.
If that is the case, then I think we are in a place where we can continue the conversation. I would want to talk about what it will take to make abortion rarer. I presume that at least they would want it to be rare. We could talk about the place that adoption and fostering might play in that but I also would want to talk about what we do to protect women and girls from rape and sexual assault. How we can provide better medical care for illness and disability. How we can better value the dignity of children with severe disabilities, as well as in some cultures, baby girls. How we can do better at lifting families out of poverty.
I am happy to have that conversation with people who, genuinely in good faith want to look at the causes of abortion and are not simply seeking to score points.