No need to argue with an atheist.

Acts 17:2-3
2 And Paul, as his manner was, went in unto them, and three sabbath days reasoned with them out of the scriptures,
3 Opening and alleging, that Christ must needs have suffered, and risen again from the dead; and that this Jesus, whom I preach unto you, is Christ.
(KJV)

From the foregoing, I encountered atheist & scoffers in a religious forum where they scoffed at the scripture, God, Jesus Christ. And through the mercies of God, I felt led to withdraw from such arguments which refused to accept the scripture as the Word of God. However, we see Paul reasoned with them from the scripture only. Atheist who reject God, Christ Jesus and the Scripture, it of no use trying to reason with them out of the scriptures.

Acts 17:1-9 PP7

3. He reasoned with them out of the scriptures. They agreed with him to receive the scriptures of the Old Testament: so far they were of a mind. But they received the scripture, and therefore thought they had reason to reject Christ; Paul received the scripture, and therefore saw great reason to embrace Christ. It was therefore requisite, in order to their conviction, that he should, by reasoning with them, the Spirit setting with him, convince them that his inferences from the scripture were right and theirs were wrong. Note, The preaching of the gospel should be both scriptural preaching and rational; such Paul's was, for he reasoned out of the scriptures: we must take the scriptures for our foundation, our oracle, and touchstone, and then reason out of them and upon them, and against those who, though they pretend zeal for the scriptures, as the Jews did, yet wrest them to their own destruction. Reason must not be set up in competition with the scripture, but it must be made use of in explaining and applying the scripture.
(from Matthew Henry's Commentary)

So if the Spirit of God grants them mercy good, if not… let the scripture be the judge.