Thanks very much Venerable! Yes, I do notice that trend of creating some hypothetical questions in order to find the loop holes. That was exactly what happened to me when I was discussing dhamma with my friend. He was not a Buddhist, so the idea of kamma does not really appeal him, what more garuka kamma.
Perhaps my explanation to him was not very accurate when he asked me which is worse- killing one's mother, or killing multiple people or a hundred million people. From what I understood, I told him the former is worse, because in my opinion, mother is the most benevolent and noble person to us, without her, we would not be able to see the beauty of this world, or even worse, without her, we wont be able to get this precious human body and have a chance to practice and realize the dhamma. Furthermore, every single mother who conceives us takes much pregnancy and labor pain for a total of 9 months, and if she does not love you, she wouldnt want to bear that kind of pain for 9 months and would just abort you off. So, no matter what, deep inside a mother's heart, she still loves you. It is maybe the approach is wrong or at the outer appearance, she appears to be cruel. Thus, to kill such a person who has done so much for you is definitely the most ungrateful thing to do, hence why it is said to be the most weighty-unwholesome kamma. But I was just being swept off for generalizing all mothers to be the same.
On another separate question, if a mentally unsound person kills his mother (something which is quite common today), do we call this as garuka kamma as well? How about a person who is under alcohol influence? Will the case be the same too?