"It is a moral fact that doing gratuitous injury to others is always 'bad'."
Ok, that's what I thought you meant. A moral fact is another way of saying based on my opinion, belief, view of the universe, desired outcome etc etc doing gratuitous injury is always bad. Incidentally, my moral compass would agree with that statement.
The way you originally stated it seemed as if you were of the school of thought that there were certain moral absolutes which I don't believe there are. All morality from wherever it springs is a human and social construct and not scientifically verifiable. Physicist Sean Carroll argues that morality cannot be a part of science...and that the scientific method cannot answer moral questions. We don't have a periodic table of virtues and it is evident by the vastly different views of morality held by different cultures that it is a moral fact because we make it so.
I can understand when people echo Dostoyevsky's "If God does not exist, then everything is permitted, " the affirmation made by the character Ivan Karamazov in the The Brothers Karamazov. If one can escape from the law men and know they will never be judged, will they still behave morally? The lawlessness that often accompanies a breakdown in social order can certainly make one wonder if humans are truly moral creatures. The old saying is that civilization is three meals away from anarchy. I have seen the truth of that up close and personally.
The counter argument being that the fact that we have the capacity to create norms and law gives us proof of a moral consciousness independent from any supernatural source. Or is that simply each person's desire to be secure in their persons that they agree together that anything that someone else does that injures me is therefore wrong?
I'm splitting hairs here as an intellectual exercise, as I mentioned above my moral compass is pretty traditional by current American standards. We holding these truths to self-evident and so forth, but if there is no supreme being handing out moral absolutes then I can understand where people might feel that in the absence of said supreme being and fear of human punishment that morality might be pretty flexible and why shouldn't I do whatever the heck I want.