Following is a very simple, but irrefutable argument that you can use (in various forms) against materialistic atheists (the vast majority of atheists) when debating virtually any topic related to atheism, theism, evolution and creation (e.g., morality, epistemology, fossil evidence, Biblical veracity, etc)...
The atheist will naturally argue that their position is true/right, and that yours is false/wrong (whether they argue this explicitly or implicity is irrelevant). And therein is your opening for an easy defeater. You can argue as follows:
Obviously you feel that you're right and I'm wrong. But as a materialist, by what objective standard of truth are you able to make this judgement? How do you determine and separate truth from falsehood and right from wrong?
You must have an objective standard of truth or there'd be absolutely no point in arguing for the truth of your claim (or evidence), in which case you're merely spinning your wheels and arguing over what we could never know to be true! (We might as well blow milk bubbles together or do something equally meaningless if this were the case.)
To deny that a standard of objective truth exists would be contradictory to your behavior, because you've clearly been arguing for the truth of your claim. Contradictions are illogical, meaning that for you to deny truth after having just argued for it would be illogical. Even if arguing your opinion (which is what your argument amounts to without objectivity) you must believe that it is minimally based on truth since no rational person seriously argues completely arbitrary things in this context. One man's opinion is no better than another's if objective truth does not exist.
Now here's the problem: There is no objective standard of truth in the material worldview! If materialism is true, then we're ultimately nothing but molecules in motion (MIMs). If your MIMs lead you to conclude that any given claim is "true" while another person's MIMs conclude the exact opposite (truth vs. falsehood), there is absolutely zero logical standard (i.e., plumb line; arbiter) by which to determine whose MIMs are correct. Thus it is logically impossible to determine truth about anything without a transcendent ultimate standard; One who knows all and can enable truth in our minds.
So unless you can provide an objectve standard of truth from your material worldview that exists outside of "the human plane" (which is impossible), your argument is moot. My worldview can account for truth while yours cannot, I'm afraid.
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