I agree with you, and I think the author does too. He was stating the supposed reasons for incarceration (he states 'supposed' explicitly). Given the definition

I agree with you, and I think the author does too. He was stating the supposed reasons for incarceration (he states 'supposed' explicitly). Given the definition of supposed is: "generally assumed or believed to be the case, but not necessarily so.", I think those were fair statements. Especially since the focus of the article is how incarceration is not effective at achieving its goals.