Have I really underestimated the inferential distance so much? I'm curious, is there anyone reading this who could follow the reference?

It is, in fact, a logical deduction from straightforward premises. Moreover it is one that I don't particularly care about as more than a curiosity.

Stepping back and looking at it objectively, do you not think a more likely conclusion to start with is that there are non-suicidal rational thinkers living in France, who just don't happen to form a majority?

Technically no. The probability I assign to less than 50% of the population of a country being rationalists is somewhere in the ballpark of a mere 99.999%. That is less than 1. I say 'technically' because the comparison is not relevant.