In general, the worry about Joyce’s debunking argument is similar to the worry about Street’s: unless we start out already assuming (against the realist) that there are no knowable moral truths, it is hard to see why we should accept Joyce’s premise that we possess a complete non-moral geneaology of moral judgment, and hence that it is explanatorily superfluous to posit moral truths. Whether or not the non-moral geneaology is complete is precisely what is in question in ongoing metaethical debat