First you completely missed the point of that question. You initially speculated why people should care if it is not directly harming them, this is a clear and obvious example of people caring about something that doesn’t directly harm them. Showing that your initial objection was unfounded.
Second you immediately abandoned the bodily autonomy argument, just like I pointed out you would.
“Unless my Immoral things is infringing on your rights”
Circle back to the serial killer. They aren’t infringing on my rights, how dare I object! What right do I have to enforce my morality on them?
Obviously it is permissible to enforce morality regardless of whether or not the subject likes it. The question is simply how to determine if the morality is correct, i.e consistent and well-founded.
“Moral arguments can form opinions not legislation”.
Nope, that’s literally all that legislation is. A moral system is something that determines whether or not something is good or bad. If a law declares that some action should be taken or certain actions are to be prohibited it is enforcing a moral system. (That moral system may be wildly inconsistent and contradictory but it is still a moral system).
There seems to be this popular notion ( outside of moral philosophy) that morality is somehow empirically derived. Unfortunately no matter how much you watch someone die, you will never gain any information on whether that circumstance is bad or good. Empirical facts may aid in classifying actions, but they do not create the requirements for the categories themselves. For instance you have a moral system that says that actions with property X are bad, you may use empirical facts to determine that action Y has property X and you can therefore determine that action Y must be bad. Without the initial premise that actions with property X are bad, you could observe Y and any other action and have no ability to determine if they are good or bad.
“In the direction of academic studies”
Not so much studies as arguments, since moral philosophy is not really an empirical field, but rather a rational one. You can find them in many ethics journals. A notable paper is “Why Abortion is Immoral” by Don Marquis, and if you read any papers in favor of abortion or infanticide there is generally a paper rebutting it.