Islam claims to be the final revelation of the same God that gave the tablets to Moses, and the same God who sent Jesus (though they claim Jesus is a prophet - not the Son of God). They claim that Islam is built on top of Judaism and Christianity - as though it is somehow the superior final word.
That said, they need to be forced to answer/explain how the ‘turn the other cheek’ teachings of Jesus are compatible with the violence of Islam. They need to answer why taqiyya (condoned lying) is compatible with ‘thou shall not give false witness). They need to explain why a loving God would condone the evil they've visited among others.
My point was once of practicality. They are not going to have an "Aha" moment no matter how much proof in front of them. You can't stop an ideology no matter how flawed that ideology may be.