It doesn’t matter how many. 1000 idiots still think like idiots.
If you want any “study” to gain actual scientific credibility, you must provide their exact, precise, scientific definition of the concepts they are trying to measure. Saying “well everyone knows what morality is”, is NOT scientific. And any study that claims to be scientific yet didn’t even know that one fact, isn’t worth anything at all, no matter how many such ignorant people attempt the same task.
I haven’t seen that you have any special knowledge of the “Philosophy of Morality”. The fact that you haven’t given a precise definition for “Moral Behavior” and for “Evil” (only a vague one), implies that your standard for “knowledge” is pretty low. As a philosopher wanting to deal with science, you should be far more pedantic. You cannot ask the scientists to do your job for you or even understand why you do it.
Perhaps it is just me but I tend to go with the motto of Science, “Nullius in Verbe” (take no one’s word). I don’t really care what Kant might have said or anyone else from 100s of years ago. The question is whether you can present the case yourself.
First, what my credentials might be is completely irrelevant because I am not the one making the claim, but rather merely checking your logic. Secondly, as I stated, “Nullius in Verbe”, so who cares what my credentials or anyone else’s might be? I don’t care what your “credentials” might be. Philosophy is NOT about worshiping idols and props.
If you want to convince me personally, you absolutely must provide an unambiguous, precise definition of the critical words and concepts you are using. After that, it is usually merely an issue of coherently maintaining your language (aka “Logic”) . It doesn’t matter what the subject is.
In case you are wondering, morality is a code of ethics established as a base standard of behavior to be expected from all members of a selected group. “Universal morality” doesn’t make a whole lot of sense because the grouping implies that all living creaturs are to be expected to obey a code of ethics.
Infants, as Arminius has pointed out, are not part of the specified group for which morals and evilness would apply.