Objective Morality

First of all, I still don't get the "justice" part on killing babies, the elderly, and livestock.

Anyways, there were talks about objective vs. subjective morality when I saw 1 Samuel 15:2–3 in the Bible so I asked a question:

"If the killing was commanded by god, will it make killing good?"

I asked this question since I know that Christians (or theists in general) believe that morality is objective. I was surprised to find out that most Christians seem to be unfamiliar with the issue regarding objective morality. 

According to Christian apologist Norman Geisler in the book When Skeptics Ask, an absolute moral obligation is an objective (not subjective) moral duty. That simply means we derive our morality on something - and let me guess. That something is god. God defines whether the action is good or bad. So, according to most Christians, our morality is derived at god's commandments and where else can we find it better than on the Ten Commandments. Moral duty is therefore objective because god (who is always good) commanded you to do it. 

Therefore, if god says "Thou shall not kill" (or murder, depending on what bible translation you are using.)then killing is an evil act.

But then there's 1 Samuel 15:2–3 in which god commanded the killing (or murder) of infants, and the elderly. Which brings me back to my question: "If the killing was commanded by god, will it make killing good?"

Some Christians agree that it makes killing good or justifiable.

Wait? That makes morality arbitrary, not objective. That makes good "good" depending on god's commanding it to be "good" and not through the action itself. 

AND objective morality SHOULD EXIST because their god requires it! Remember, one of the arguments on the existence of god is the existence of objective morality. If objective morality doesn't exist, then this SUPERNATURAL LAW GIVER also doesn't exist.

Facing 1 Samuel 15:2–3, most Christians try to sweep away the issue. Some even became subjectivist themselves by stating the action of killing depends on the situation. This statement unknowingly wins the case for those who believe that morality is subjective. There are a lot of red herring in which most commenter tried to change the subject matter by inserting irrelevant issues to distract the original question like the difference between killing and murder, but I always try to bring it back to the original topic. I even read a guy saying 1 Samuel 15:2–3 was a military operation. So when genocide did became a military operation?

I guess it all brings down to the fact that morality is really all about a person's opinion.