Mansfield knows his stuff. He's been a professor for 50 years, and he's smart enough to combat inflation with a relatively non-punishing system: “In recent years,” said the Boston Globe, “[Mansfield] himself has taken to giving students two grades: one that shows up on their transcript and one he believes they actually deserve. 'I didn’t want my students to be punished by being the only ones to suffer for getting an accurate grade,' he said.”
Everyone likes to receive a decent grade, especially if you don't have to work that hard for it. But yeah, there's an issue when every one is more or less the same. (Even though, literally, the day you graduate will be the day your GPA ceases to matter.)
Mansfield's done Harvard a favor by pointing out how hilariously far its inflation problem has gone. But his point could be refined a bit: Grade inflation really only affects liberal arts students. Ask any pre-med or engineering student—they'd kill for an A- to be the norm.
And this isn't a Harvard-specific problem. 43% of all grades in the United States are now A's, up from 15% in 1960 and 31% in 1988. We're all totally fucking coddled.