Question: The issue has crept up on me slowly over the last several years. I am increasingly aware of the massive debt that many of my students are taking on, debt which is far beyond the sort of debt that I incurred as an undergraduate in the 1980s. Because of this, in recent semesters I have found it somewhat difficult to fail students. Instead of simply asking myself "does this student deserve to fail this class?", I find myself asking "does this student deserve to have their life ruined?" In many cases (e.g. students who are already on academic probation) this is not much of an exaggeration. It is a very bad situation to find yourself in your early 20s with no college degree but $30,000 in debt. In some cases, I am aware that a decision of mine might be a contributing cause of a student ending up in just such a situation. I can no longer regard a failing grade as a relatively minor matter (like a speeding ticket).

How do professors reconcile their de jure role as guardians of academic integrity with their de facto role of being (at least in part) responsible for their students' economic future?

Answer: 
Something other answers did not yet address - by giving unfairly good grades to undeserving students, ***you are dramatically, and unfairly, penalizing good students***.

Students - in large part - choose to attend a university based on its academic reputation. Perhaps, paying premium.

If your lax grading methods graduate unfit students instead of failing them, this will materially affect the successful student's reputations as graduates of your school, since the employers or graduate schools would have no way of knowing if someone graduated your program because they were a good student, OR, because you took pity on them. So, everyone will be tarred with the bad reputation and that would negatively affect their lives and careers.
I generally design my exams so that even a student with relatively limited understanding of the course can pass. I would really only consider a student who has achieved the highest grade (> 80%) to have a good understanding of the material, and I often see just-passing exams (50-60%) where I think that the student really had no idea, but somehow managed to scrape together enough marks to get over the line.

Armed with that viewpoint, when I see a student who fails, I think they must have really deserved it! So I don't feel too bad about failing them; they need to put in some effort to fail my course!