I've always thought they were pretty well defined.
- stealing is wrong...murder is wrong...infidelity is wrong...etc
On the other hand, you can explain in plain, rational English (without resorting to religion) why you think abortion is immoral and destructive to society
No you can't because religion, in this case the Law of God, is the prevalent factor in determining just why abortion is wrong.
For you it certainly is. For others, it may be different. It is possible, and not even difficult, to make a strong case against abortion without religion.