Kagan has a fun new paper in Philosophy & Public Affairs, 'Do I Make a Difference?', addressing two kinds of cases where act consequentialism seems to condone collectively bad outcomes because each individual's contribution appears to make no difference.
The first kind of case, what Kagan calls "triggering" cases, I've previously discussed under the title "chunky impacts". This involves cases like buying meat, where it may seem that any individual choice makes no impact, but in fact there's some threshold in place such that (all else equal) there's a small chance of us having a proportionately large impact, balancing out the expected utility (so that, e.g., the expected outcome of buying a chicken = 1/N * N = one chicken death).
The second kind of case involves allegedly imperceptible differences adding up to a large total impact. Here Kagan stresses (as I did in my post on the self-torturer puzzle) that -- as a matter of logical necessity -- there must be some difference in phenomenal feel between some two adjacent states in the sequence, even if this difference isn't directly perceivable (when limiting oneself to pairwise comparisons).
[It's too bad that I can't put those two blog posts on my CV and have them count for as much as a publication in P&PA! ;-) ]
It's a nice feature of Kagan's paper that it brings the two kinds of cases together, falling as they do under the same broad umbrella of cases of bad results (from people's actions) where it seems that no individual action has negative impact. With that broad umbrella of worries in mind, it occurs to me that an interesting third class of cases in this vein are the coordination problems that Donald Regan's cooperative utilitarianism addresses.
The thing I find most interesting about Regan's work is that in the end we're forced to acknowledge that it's possible for everyone's acting (objectively) rightly to be a bad thing. This shouldn't be taken as any kind of objection to consequentialism, however, as I hope the linked post makes clear. Rather, it should temper our ambitions and expectations for what we hope to get out of a moral theory.