Here is a passage you might not think to apply to apologetics. Second Corinthians 6:14-18 tells us not to unite with unbelivers which I think includes how one defends his beliefs.

"Do not be bound together with unbelievers; for what partnership have righteousness and lawlessness, or what fellowship has light with darkness?"

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Richard Kairelis
Westminster Reformed Presbyterian Church, RPCNA (Prarie View, IL)
Chicago, IL