In the way Sudafed is meth. Agency MBS’s never faced solvency questions. Unrated mortgage-backed securities and whole mortgages did. You are argued the Fed bought toxic crap off banks. It didn’t. It bought the cream of the crop, giving banks liquidity with which to address the rest.

The difference between mortgages and agency MBSs is entry-level finance. You don’t need to know it. But you should understand your circles of competence well enough to know not to debate it.