I don't think your experience here is that uncommon, since the first paper calls on students to problematize, a rhetorical strategy that's totally foreign to most college freshmen. It's something I recall us talking about in a monthly meeting last year, and my explanation (which you can buy or not) was that our students are immersed in two rhetorical genres: one the testimonial narrative (on panel shows, human interest news stories, etc.), and the other the political opinion (talk radio blowhards, newspaper editorials, etc.). Those dominant rhetorical forms are connected in a number of ways, but most importantly for our students, they have no need for either critical reflection (i.e. on facts or context) on the part of the speaker/writer, or a critical disposition on the part of the listener/reader.
At any rate, rather than it being a primary/secondary matter, I'd suggest that the papers reflect the students' rhetorical dispositions--or, one might say, what they got out of the text and instruction thus far. I've found though that because problematizing (what the Allyn and Bacon Guide calls "wrestling with complexity" ad nauseum) is the essential rhetorical orientation for which the book is arguing, and on which the students will be working for the term and their college careers, the first paper is an opportunity for students to get their feet wet.
OK, a couple of practical suggestions (you may already be doing one or both of these): one, give students a week (or so) to revise and resubmit their papers after revisiting the chapters and your comments. Two, encourage students to resubmit the paper in a portfolio at the end of the term, so that the first and the last papers "frame" the course and can document the progress they've made--thus you can value student progress and acquired rhetorical sophistication more than the content of the first paper in isolation. I'm sure others will have more (and perhaps better) advice for you as time goes on. We can also think about how to incorporate your experience into the year's theme of interacting with students.
That's about it for now. Comment at will...