Success in much of the business world requires you to play by the rules of the business system, which may be as capricious, arbitrary, pointless, stupid, and orthogonal to relevant knowledge [1], as success in the school system.
For every hiring manager who takes the approach that anyone putting their GPA on their resume is an asshole or an idiot, there's three others who think that there's something wrong with a junior applicant who doesn't put their GPA on their resume.
Unless you tell the applicant what you want to see, they have no idea which of these two hiring managers you might be. Instead of downmarking people for having the audacity to present this information to you, perhaps you could just ignore it?
[1] Which the hiring manager in this thread has unironically demonstrated.
Without any evidence to back up your claim I could just as easily claim that for every hiring manager who cares about seeing a GPA on a resume there are three others who think there's something wrong with an applicant with any experience who does put their GPA on their resume.
For every hiring manager who takes the approach that anyone putting their GPA on their resume is an asshole or an idiot, there's three others who think that there's something wrong with a junior applicant who doesn't put their GPA on their resume.
Unless you tell the applicant what you want to see, they have no idea which of these two hiring managers you might be. Instead of downmarking people for having the audacity to present this information to you, perhaps you could just ignore it?
[1] Which the hiring manager in this thread has unironically demonstrated.