In college, I dated a woman who was, it turned out, quite seriously mentally ill. She had Borderline Personality Disorder, which led to her engaging in reckless sex, spending, etc. She cheated on me. It was awful.

How much does the mental illness — the fact that there’s a label attached to her collection of behaviors — excuse those behaviors? Actually, let’s ignore the actual diagnosis and the actual label. Let’s just take it as given that the underlying understanding of her mind is correct: that it is harder for her to avoid certain risky behaviors than it is for the rest of us. Let’s suppose that she could, if she tried very hard, avoid those risky behaviors, but that it takes a lot more work for her than it does for others. How justified are we in thinking ill of her? How much does the illness excuse?

Or take another, quite different situation which I think shares a lot of similarities with the above. Lots of people live in car-dependent places. Consequently, their daily lives involve their inflicting more damage on the environment than do those who live in denser, more-walkable areas. On the one hand, we may want to pass moral judgment on them: their actions are harmful to all of us, and to our children. On the other, what leads many people to live in car-dependent areas are structural problems, namely that mass transit in this country is poor and that housing in dense, walkable areas is expensive. People could, perhaps, choose to live where their environmental damage is lower, but that choice comes with a cost. In some places (I’m thinking of San Francisco here), the choice is too costly to be reasonable for many people. So they buy a car, live out where the land is cheaper (and where their children can play in the backyard, etc.), and harm the environment more than they would in the city.

The similarity between these two situations is that the more-virtuous choice is costly. In some cases it may be prohibitively costly. The mentally ill person may be aware of the damage he or she is inflicting on others, but the biochemical hurdle may be too high to get over. The person living in the suburbs may be able to move closer to the city, but only by swallowing a majority of her income in rent. Yes, in both cases they’re making a “choice”, but it’s a choice in which their hands are largely forced.

Past some extreme, I think many of us intuitively forgive people who misbehave, when their misbehavior seems to come from forces beyond their control. When we hear that a drug dealer chose that path because his community offered no legitimate paths to earn a decent income, we’re willing to forgive — even though he could, with effort, probably have found a legitimate path out. At some point we acknowledge that the effort exceeds what can reasonably be expected of a human being.

At the same time, our hands are always, to some degree or another, forced. I’m born into my circumstances and you’re born into yours. I’m born with my biochemistry and you’re born with yours. Not all behavior is forgivable. Biochemistry doesn’t excuse everything.

Is there just a threshold above which we implicitly forgive people their trespasses? Certain innate limitations — your society denying you a decent legitimate wage; a mental illness for which you’re heavily medicated; a built environment that makes walkable living unattainable for all but the wealthiest — may forgive a lot of behavior that we’d otherwise frown on.

Another way to look at it is that human behavior isn’t one-dimensional: the choice isn’t between living in the suburbs and living in the city; you can choose to live in the suburbs so long as city life is unattainable, and also fight like hell through your city and state governments to ensure that city life becomes affordable to those of lesser means.

I have no particular conclusion here. It occurs to me that actual moral philosophers, who actually know what they’re talking about, have probably written on this topic in an interesting way. I’d love some pointers.