You are right that "harming" someone is not a sufficient reason to ban an action. And as others have pointed out, researching a company carefully causes the same kind of "harm", and certainly shouldn't be banned. My intention was to refute people (like in the article I linked) who argue that all market participants benefit from and insider trader's transaction.
Once we see that this isn't the case, it becomes necessary to do a cost benefit analysis to determine the true effect of allowing insider trading. But as you say, this should be done on a utilitarian basis, not on some imagined "rights" of the counterparty to insider trading. (EDIT: I don't mean to imply that economic analysis from a utilitarian POV can't clarify what we should think of as people's rights, but rather that as you said, causing someone else to have a negative outcome does not prove that someone's rights are being violated)
Once we see that this isn't the case, it becomes necessary to do a cost benefit analysis to determine the true effect of allowing insider trading. But as you say, this should be done on a utilitarian basis, not on some imagined "rights" of the counterparty to insider trading. (EDIT: I don't mean to imply that economic analysis from a utilitarian POV can't clarify what we should think of as people's rights, but rather that as you said, causing someone else to have a negative outcome does not prove that someone's rights are being violated)