Can student comments help solve a problem that student ratings helped create? We argue that the comment section of student ratings of instruction (SRI) offers a rich site for studying student perspectives on teaching and learning, particularly how students define and value course and instructor difficulty. Employing rhetorically grounded approaches to computer-assisted corpus analysis, we compared 4,600 RateMyProfessor.com instructor profiles meeting the criteria of 1) instructors with high difficulty and high overall quality scores or 2) instructors with high difficulty but low overall quality scores. We identify recurring argumentative patterns in both corpora. In contrast to SRI scholarship which often assumes students favor ease over all other course characteristics, we see commenters providing a more nuanced evaluation: condemning artificial forms of difficulty but commending authentic ones. Our findings contribute to discussions of student perspectives on learning and their relationship to course evaluations. While we note SRIs should never be the sole means of evaluating faculty, the results offer evidence in support of the validity hypothesis in SRI scholarship and provide avenues for helping faculty better understand their course evaluations and students.