Vagueness and Making a Difference
Do you make the world a worse place by purchasing factory-farmed chicken, or by paying for a seat on a transatlantic flight? Do you have moral reason to, and should you, refrain from doing these things? It is very unlikely that any individual act of either of these two sorts would in fact bring about a worse outcome, even if many such acts together would. In the case of factory-farming, the chance that your small purchase would be the one to signal that demand for chicken has increased, in turn leading farmers to increase the number of chickens raised for the next round, is very small. Nonetheless, there is some chance that your purchase would trigger this negative effect, and since the negative effect is very large, the expected disutility of your act is significant, arguably sufficient to condemn it. This is true of any such purchasing act, as long as the purchaser is ignorant (as is almost always the case) of where she stands in relation to the ‘triggering’ purchase.