I have written about this subject before, but I just can't help but to find the argument from morality extremely strange.
The reason for this is that I have lived all my life in northern Europe, and I have a lot of experience on Christianity here (and the many denominations of it here), for over 30 years, and I have never, not even once, heard this argument being presented.
It wasn't until I started watching videos and reading blogs from American skeptics that I first heard this argument, and heard that seemingly this is a very popular argument among religious people in the United States, who seemingly think that it's an extremely good one.
When I first heard the argument, it sounded extremely silly. I have several good friends who are devoted Christians, and when I told them about this argument, they found it a strange argument as well (as incredible as that might sound to Americans.)
The truth is that this argument is basically completely non-existent in Europe, and most people, even devoted Christians, who hear it find it strange (at least if they are smart enough to understand it.) Or at least that has been the case for a long time. (Unfortunately it seems that in later years American creationism and apologetics is getting foothold in European Christians, and their nonsense is starting to spread here as well. You still don't hear this and other equally silly arguments here much, but I have the impression that they are steadily getting more popular.)
The major reason for this is, I think, because something like 85% of northern Europeans are secular. (Similar numbers are true for many other European countries as well, but the percentage tends to become smaller the more south we go.)
Many American Christians live in a social bubble where they can pretend that the rest of the world doesn't exist. They get to keep this false notion that the only thing stopping the country from sinking into total chaos is because the majority of people are Christians. In other words, most people behave in a socially acceptable manner because they are Christians, and atheists are a very small minority, and thus cannot cause much trouble because all the Christians are keeping them in check. Thus they can easily come up with silly arguments like "atheists have no moral values, and have no problem in killing, raping and pillaging, because they don't believe in a higher authority."
The situation is completely different here. Being secular/atheist is the norm, the majority position. You can quite safely assume that the average person is secular. Being deeply religious is the exception, the odd-one-out. And quite clearly society keeps going as normal and has not sunk into total chaos and destruction. Therefore the argument in question would just sound silly because it's clearly just not true. That's why not even Christians present it. It would be like "huh? What the hell are you talking about?"
This is why it just keeps sounding really silly when I keep hearing this argument being made over and over mostly by American apologists and creationists, as if it were some kind of good and convincing one.