Here's an after thought.
There could also be the sense that he is trying to just state that faith is irrational because it acts upon that which it cannot see. But it is not that faith see nothing at all, just does not see the fulfillment of what was promised yet.
Still it would be an Arminian position to state that faith is the source of regeneration and belief. So to think it irrational that one can have a rational approach to unbelief, would mean that the reasoning mind, trying to present something to an unreasoning mind, is irrational (the living talking to the dead is irrational, But see Ezekiel 37). He may be then arguing that because faith is not seeing, and thus irrational (in his definition), it is also irrational to try to get someone who is unbelieving to rationally see the same thing. But God states that He will not work according to men’s wisdom, but according to His own, which makes men‘s wisdom foolishness and irrational at times.
Positive apologetics do not rest it's assurance of success in it’s pure mental reasonings, but makes the best mental conclusions (reasons) it can, and leaves the rest to God (regeneration and the resulting faith). More so in preaching, one may plant and another water, but God gives the increase.
