First, I wouldn't want to naysay the idea that unemployment is a vicious cycle, because it intuitively is. But: this analysis is based on resume callbacks. Something that I think is as true as the "damaged goods" stigma is that most Americans do not know how to market themselves during job searches. If your only access to the job market is through a mechanism that is designed to extract basic facts from a resume and screen based on that, and there's high unemployment and so increased demand for every position, it stands to reason that unemployed people are structurally disadvantaged when competing for jobs via resume blasts.
Second: Six months, you say? Can any of us think of a cohort of job seekers that routinely needs to contend with 6+ month employment gaps? I wonder, maybe, just maybe, do you think that has a powerful "objective" stigma attached to it disproportionately often might find it difficult to compete equitably in the job market? I wonder which 50% of the population I might ask to find out more about this.