Prefacing a criticism with "XXX is an upstanding person, but..." is just shorthand for saying "I am aware of and actively trying to avoid ad-hominem arguments,

Prefacing a criticism with "XXX is an upstanding person, but..." is just shorthand for saying "I am aware of and actively trying to avoid ad-hominem arguments, and genuinely believe my concerns are with the institution/setup/company/regulation and not with individuals." I think it's a legit rhetorical device.