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: 
I think you are trying to assume too much responsibility.

The way you grade your students (assuming no malicious intent on your part) is not what is (possibly) causing their ruin. What might be causing it (besides, perhaps, some bad decisions of their own) is the system which forces them to go into debt or does not provide them with sufficient opportunities to study properly (e.g. by having them go to bad schools, or forcing them to work long hours in a part-time job).

You are not directly responsible for any of this.

Indirectly, you can try to change the system. I can think of a couple of ways to do it:

1. You can support (or even start) political initiatives which aim to change what you consider to be unfair.
2. If you think your job is part of the problem, you could quit, and look for a different job which would have less of a bad impact (e.g. a worse paid job at a place with lower fees).
3. You could do something to actively sabotage the system.

I think your suggestion (passing students who don't really merit a passing grade) falls under the sabotage category. Indeed, by passing students regardless of their merit, you undermine the whole system --- the more teachers at your institution do that, the less value a passing grade will have. At the logical conclusion, the whole higher education system would collapse, and something better could come up from the ruins. Maybe (but probably not).

Either way, in the interim, this would harm all the *other* students (who do merit a passing grade) by diminishing their accomplishments, other people (when the "passed" ones get a job they are not competent for, perhaps instead of someone more qualified), and possibly the ones you wanted to help (by pushing them to an ill-chosen career path).

I think ideally, the first solution I have mentioned should be the best, and sabotage should only be used as a last resort.
All things in life can cause you economic ruin these days. House mortgages, car loans, hacking, frauds. 

It is basically a society based on debt-based servitude where the banks are our overlords. You are likely just one well-meaning person in this huge mess and likely cannot affect this fact. As far as I know you also can not affect what these students future employers will base their decisions on. 

It is not your moral obligation (nor is it even within your power) to try and steer where these students end up. It is the privilege of these debt overlords to do.

Your job is to teach and to grade. Do your job, peasant.