What do you mean by "wrong?" And why should logic trump practicality? Besides, rightness and wrongness are value judgments. They have nothing to do with logic.
M/D/Y seems to be the most practical because it reflects how dates are spoken in American English. It separates the date (month/day) from the year, which in many cases can be omitted, while also keeping the larger unit, the month, up front.
"wrong" was in reference to the post being replied to.
The majority of English speakers and people in general don't speak American English, so it makes zero sense to default to "M/D/Y", unless the user explicitly states to use American English, over a more logical order, ideally Y-M-D.
Pretty much all defence in this thread of M/D/Y is just American exceptionalism.
M/D/Y should never be a default for any software without the user explicitly selecting it or specifying their country.