Grade inflation and higher education

The Volokh Conspiracy » Reforming Higher Education: Incentives, STEM Majors, and Liberal Arts Majors – the Education versus Credential Tradeoff.
The pernicious bubble in higher education is not the near-runaway attendance costs, but average undergraduate GPAs that approach 4.0.

Chart from gradeinflation.com

While there is no grade inflation in the technical courses (Science, Technology, Engineering and Math, or STEM), it's shot through the roof in the humanities. Why one and not the other?
Basically, STEM schools or departments are in worldwide competition with each other, and their reputation rests on their top-performing graduates. Hence, introductory STEM courses are designed to weed out the poor and average performers, and that means the classes are conducted at a pace that students with merely above-average math skills can't keep up. (I also wonder whether STEM professors know they can't curve grades for people who might be designing long-span bridges, power plants or airliners.)

This is not to say, however. that STEM schools have been immune to grade inflation over time.

As for humanities departments, there is no inter-school competition. Harvard's history department does not compete with Oxford's, or for that matter with State U's. If a student wants to get a BA in history - or philosophy or English Lit, whatever - it really is not much relevant what the name of the school is. The reason is that humanities departments have become almost useless for graduating bachelor holders who are immediately employable in their major. So undergraduate humanities schools are really just prep schools for Master programs or law schools. 
That explains the grade inflation in humanities departments. Grade inflation has not corrupted the system, grade inflation is the system. And the more comparatively worthless a bachelors humanities degree is for postgraduate employment, the higher its average GPA is. That's how those departments justify their existence to the larger university and how they attract students to select those departments as majors. 
Grad schools don't care where their applicants matriculated. Grad schools consider nothing at all about a student except his/her GPA. A 4.0 at State Cow College in global civilization studies is far more credentialing for admission to a grad school than a 3.5 in physics from MIT. Grad schools don't care where the 4.0 came from or what its major was. They just want the high GPA. 
So a college student choosing a major should determine real quick whether he is grad school bound, and if so, select a major with the strongest record and reputation for grade inflation. That such a major is almost certainly going to be worthless for job seeking and will usually be free of intellectual content (like, oh, womyns studies) is irrelevant. Just get as close to a 4.0 GPA as possible. It's all that matters.
That's a short summary, of sorts, of prof. Volokh's assessment. But it's not altogether in line with a more in-depth study online here. However,

The author believes that the resurgence of grade inflation in the 1980s principally was caused by the emergence of a consumer-based culture in higher education. Students are paying more for a product every year, and increasingly they want and get the reward of a good grade for their purchase. In this culture, professors are not only compelled to grade easier, but also to water down course content. Both intellectual rigor and grading standards have weakened. The evidence for this is not merely anecdotal. Students are highly disengaged from learning, are studying less than ever, and are less literate. Yet grades continue to rise.

Then there's this:

To avoid getting an "incomplete" for the course, Ms. Zhou withdrew before the lab ended. Since switching majors she has earned almost straight A's instead of the B's and C's she took home in engineering.

Students who drop out of science majors and professors who study the phenomenon say that introductory courses are often difficult and abstract. Some students, like Ms. Zhou, say their high schools didn't prepare them for the level of rigor in the introductory courses.

Overall, only 45% of 2011 U.S. high-school graduates who took the ACT test were prepared for college-level math and only 30% of ACT-tested high-school graduates were ready for college-level science, according to a 2011 report by ACT Inc.