Wow, Kelton did really say that. I never did finish reading her book, I found it much less convincing than Mosler's or Mitchell's. Many MMT'ers consider themselves to be the true heirs of Keynes, so embracing things that so directly contradict Keynes...

Like any field, there are different sides to it. Krugman and Cowell are both mainstream economists, but they disagree on a lot.