youre right we shouldnt use our own seichel in searching for reasons. but reasons are of critical importance in poskining shailos of course, for those that have daas Torah and are able to paskin.
and reasons are also valid in discussions like this when based on daas Torah. IF the reason given by mw13 IS valid, with a mikor, then it is reasonable to use it as a basis for an argument. IF it has a Torah source.
but your point: “The reason is that Hashem said so.” is of course a beautiful point, and the essence of Emes, that we should always try to keep in mind. thank you for writing it.