I agree with Mukunda, if they want to argue then that's their problem, you don't have to buy into it.
They are coming from the view that Buddhism is a direct competitor to Christianity just because they are both world religions. I don't agree, I think they are trying to achieve quite different things therefore arguing one against the other is meaningless.
It would be like an accountant arguing with my beliefs because they don't conform to the fundamentals of accounting, or a musician because they don't conform to rules on tone, pitch, melody etc.
"Proper effort is not the effort to make something particular happen. It is the effort to be aware and awake each moment." - Ajahn Chah
"When we see beyond self, we no longer cling to happiness. When we stop clinging, we can begin to be happy." - Ajahn Chah
"Know and watch your heart. It’s pure but emotions come to colour it." — Ajahn Chah