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.
“Peace is within oneself to be found in the same place as agitation and suffering. It is not found in a forest or on a hilltop, nor is it given by a teacher. Where you experience suffering, you can also find freedom from suffering. Trying to run away from suffering is actually to run toward it.” ― Ajahn Chah