I have taught Intro Economics maybe 30 times in total. (I started very young).
Forget about the A students, because there aren't many of them. (We don't all have massive grade inflation.) Think about the C students. And forget about the Economics majors, because other people will teach them after you. Think about the students who will only take this one course in economics. And think about what they will remember, not for the final exam, but 10 or 20 years after you have taught them. What will they remember from intro macro, if they remember anything at all? Not much.The best you can hope for is a crude and fuzzy caricature.
Imagine asking such an ex-student a simple question: "what should the government do, macro-wise, to make people better off?"
The student who has been taught AS-AD will probably reply: "Increase supply? Increase demand? I'm not sure which and I'm not sure how. And should we think about inflation too? Dunno."
The student who has been taught the Keynesian Cross will probably reply: "Increase government spending!"
The first answer is nearly always a much better answer.
The Keynesian Cross should be put on The Index. It should only be taught to PhD students. But it should be compulsory for PhD students. It contains a very important insight about deviation-amplifying positive feedback mechanisms when people are quantity-constrained and use adaptive learning. And that insight is missing from New Keynesian models.
One of the reasons I really like Greg Mankiw's intro text (I was a Canadian co-author on the first 3 editions) is that it leaves out the Keynesian Cross (though it does mention the multiplier process as an aside).
My little contribution to the recent Keynesian Cross Kerfuffle.