Full Idea
The absurdity follows [from Kant's categorical imperative] that in the case of moral conflicts reason and morality require us to act irrationally and immorally.
Gist of Idea
If morality has to be rational, then moral conflicts need us to be irrational and immoral
Source
John Kekes (The Human Condition [2010], 10.4)
Book Reference
Kekes,John: 'The Human Condition' [OUP 2010], p.222
A Reaction
We can't pick one from two equals if we must have a reason for the preference, but that does not make it 'irrational' to choose one of them, when it doesn't matter which one is chosen. Taking one of the cheese sandwiches is not irrational.