I see the basic conflict as thus:
If you base your ethics on reason, then you don't leave any room for exceptions. You have reasoned it out, so to speak, that what is wrong is wrong under any circumstances. There are no exceptions or you would have rather shakey ethics.
When you base your ethics on emotions, feelings or affections, you are bound to constantly "adjust" you ethics based on how you are feeling at the moment.
You can see this in the topic of abortion: Suppose I say that abortion is wrong...but wait, my friend needs an abortion, so that's ok because she is my friend, and I like her. So it had to be done.
Stealing is wrong, and stealers should be punished. Wait..my child just got caught stealing. Ok. I'll (the parent) will pay the price, because the punishment will be too hard on my child. This could go on forever.