Whenever I speak of the “killing of an innocent person” I’m referring to publicly agreed-upon cases of unjustified killings. This isn’t begging the question because the entire point of Marquis’ argument is to begin with cases that everyone agrees constitute unjustified killings. That’s the common ground starting point. He’s in essence saying: “See that activity that you and I and everyone else thinks is super wrong? Abortion is like that.”
That’s precisely the force of the argument. Otherwise, the argument would be bizarre: “See that action whose morality we disagree about? Abortion is like that.”
What follows from what I’m saying here? That if you give me an instance of killing which does not have this agreed-upon wrongness, it obviously doesn’t apply to what we’re talking about.
Marquis would say that for the same reasons we take killing an adult wrong (in cases which we agree), we should take killing Philando Castile wrong, or killing non-combatants wrong. He could, in essence, deploy an argument in the same way toward the very cases you’re bringing up. So I don’t see how this is supposed to problematize Marquis or the concept of murder’s overridingness.
Yes, people often get this wrong or fail to apply murder’s overridingness, but that doesn’t mean there’s something off about the principle.