And why is it wrong to harm someone, then?
And why is it wrong?
And then? What makes a human more valuable than a pair of shoes I want?
See…The problem is that for proving that something (killing people for their shoes) is wrong, you have to first assume various things (that harming people is wrong, that a human life is worth more than a pair of shoes, etc…). So, your moral judgment isn’t based on some absolute which would be exterior to you, but on your preexisting moral values (harming someone who didn’t deserve it is wrong, taking something from someone is wrong, etc…).
It’s circular because each time you say : I know that A (killing someone) is wrong because it implies B (harming him) which I know is wrong. So, you’re still at the same point : you’ve now to explain why B is wrong. If you can’t or don’t it’s the same as saying “A is wrong because I say so”.
There’s no need to explain it, because once again you would say “because harming people is wrong”, “because children can’t defend themselves and it’s wrong to attack people who can’t defend themselves”, etc… Once again assuming your moral rules as a given. You’re not proving that putting a cigarette on a child’s arm is absolutely wrong, but that it is wrong according to the moral values you’re holding (and which are still not proven to be “absolutely valid”).
When you say “it’s blazingly obvious” , what you mean is “it’s blazingly obvious for all people who agree with my basic moral values”. But this is not an absolute. To be absolute it should be independant of anybody opinion. The law of gravity is absolutely true because even if I disagree with it, I will still fall. But morals can’t be absolute because as soon as people think “harming children is unimportant”, then harming people isn’t immoral anymore.
Let’s take another example. Someone can think, for instance, that there’s no circumstance where someone should kill someone else except in self-defense. For them, the death penalty is immoral. Some other people can think than a criminal must receive a punishment. For them, death penalty is moral. I assume that in this case, you understand why morals are relative. You understand it because it’s an issue on which people usually disagree.
But the only difference between the statements : “death penalty is immoral” and “torturing children for fun is immoral” is that in the first case only, say, 50% of people agre while in the second case 99,99% of people agree. But there’s no difference in nature between these two statements. None is provable. And if tomorrow 99,99% of people agree to say that the death penalty is very wrong, both statements will be on par.
You’ll note that both acts are of the same nature. In both cases you’re harming someone. But you arbitrarily decided that harming “for fun” is wrong while harming “for revenge” is OK (many people think that revenge/ “an eye for an eye” is a good enough reason to justify the death penalty). And also that harming someone below a given age is “more wrong” that harming someone above this age (or else, why would you insist on mentionning children/babies in your examples?). Which is totally arbitrary. There’s no way to prove that harming a 2 y.o. is morally worst than harming an adult. And I could argue that death, which is definitive, is worst than torture. Hence that executing a criminal is worst than torturing a baby. How could you prove me wrong?
Your error is that you think that “moral relativism” means that there’s always a way to justify an action within a given set of moral rules that you take as a given (including “harming someone is wrong” or “a human life is worth more than a pair of shoes”). What we are saying is that this basic set of rules is itself arbitrary and depending on the time and place. And even if some of these rules have been accepted by the overwhelming majority of people in the overwhelming majority of cultures, there’s no difference in nature with rules which have been accepted by only a minority of people in a minority of cultures.
You’re in fact saying “almost everybody think/feel that torturing babies for fun is wrong. That’s an absolute”. Nope. That’s only what almost everybody think/feel. An absolute moral rule would be true for everybody, whether they agree or not, and would be provable without reference to another moral rule.