Megan MacKenzie has a good, long post on the ethics of casual teaching contracts:
For the last few years in particular, there has been a marked increase in the number of sessional, casual, teaching-only, adjunct, fixed term, temporary job ‘opportunities’ listed and circulated in the usual IR job venues. These various titles and categories point to one reality: precarious labor is a permanent reality within academia. The trend has been quantified and well documented: in US in the last 30 years the percentage of positions held by tenured or tenure-track faculty members fell from 56.8% to 35.1%. In an excellent post in the Chronicle, Peter Conn declares “Full-time tenured and tenure-track jobs in the humanities are endangered by half a dozen trends, most of them long-term.” The trend is not new; however, as the race to the bottom with regard to casual labor hits a new low, what is missing from the discussion is (1) the ways that permanent staff reproduce/support casual labor and (2)the myths associated with the ‘opportunity’ of casual labor for PhD students and unemployed academics.
On a related point, I appreciate that the economics and politics associated with the academic job market are complex, but it does seem that unless you can conceive of a viable political means to expand opportunities for newly minted Ph.Ds, you ought hold off on increasing the size of existing programs.