Categorical imperative requires something to be universally moral before it is justified.
As in your actions must be moral in terms of any person in any situation. But that comes down to whether universals actually exist. Easy if you are heavily spiritual or theological, but those different religions don't exactly agree on universals.
It was a case of attempting to apply a syllogism (formal logic) to a real-life scenario which has proved impossible because things just aren't that simple. That is, unless one religion or philosophy of ethics is universally accepted, yea right!