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.
"Right effort is effort with wisdom. Because where there is wisdom, there is interest. The desire to know something is wisdom at work. Being mindful is not difficult. But it’s difficult to be continuously aware. For that you need right effort. But it does not require a great deal of energy. It’s relaxed perseverance in reminding yourself to be aware. When you are aware, wisdom unfolds naturally, and there is still more interest." - Sayadaw U Tejaniya