I can't stand that attitude. I understand it, but it is wrong IMHO. Flight school, no matter the stage, is still a filter for the fleet. Can't stand it when students show up to the FRS, or worse a fleet squadron, unprepared and should have been attrited in advanced.
But instead, we pass the trash because "no one should attrite past primary".

There's a world of difference between making damn sure the IPs didn't fail the student and so-called "passing the trash." What @ChuckMK23 is describing is precisely the opposite of "passing the trash;" it's doing a post-mortem to figure out how an attrite got so far along and how to ID them earlier next time.
There are three types of people in any line of work, Naval Aviation included: Those that can succeed with little or no help, those who have no business being there, and those who can muddle through mostly competently with some coaching. Sure, it's actually a continuum, but my point remains. If someone can't make an honest effort to milk as much as practical out of that middle third, without confusing them with the bottom third and writing them off, they have no business in any kind of instructor role.