If I were you I would ask the instructor to explain the mechanism by which a staining developer harms the emulsion of the film, or the authority on which he/she bases this opinion.

Most staining developers (and this includes PMK, ABC, Rollo Pyro, Diaxactol and Pyrocat-HD) tan as well as stain, and the tanning actually hardens the emulsion as the film is developed, making it less susceptible to damage from scratching or tearing away from the base during the final stages of processing. In other words, films developed in staining /tanning developers are actually less likely to emulsion damge than films developed in traditional developers.

I think your instructor just got it backward.

Sandy King