Fiery Cushman, Joshua Knobe & Walter Sennett-Armstrong have a paper entitled Moral Appraisals Affect Doing/Allowing Judgments on the web. Here is a description from a blog post by Knobe on Experimental Philosophy:
Probably the best way to give you a sense for the idea here is just to describe one of the studies we conducted. In our first study, all subjects were given a story about a person who ends up in the hospital. The person is being kept alive by life-support systems, but then the doctor turns off these systems specifically for the purpose of making sure the person dies. With the life-support systems now absent, the person’s life soon ends. Subjects are then asked whether it would be more accurate to say that the doctor ‘ended’ the person’s life or that he ‘allowed it to end.’
Now comes the tricky part. Subjects were randomly assigned either to the ‘morally bad’ condition or to the ‘morally ambiguous’ condition. Subjects in the morally bad condition were told that the doctor removed the life-support system because he despised the patient and did not want to use valuable resources on him; subjects on the morally ambiguous condition were told that the doctor turned off the life-support systems because he honestly believed that the patient would be better off not having to go on suffering. (This latter condition is morally ambiguous in that those subjects who are in favor of euthanasia should regard it as morally good while those opposed to euthanasia should regard it as morally bad.)
As expected, subjects in the morally bad condition tended to say that the doctor ‘ended’ the patient’s life, while those in the morally ambiguous showed a more complex pattern. Specifically, subjects who said that in general they regard euthanasia as morally bad tended to say that the doctor ‘ended’ the patient’s life, while those who said that in general they regard euthanasia as morally good tended to say that he ‘allowed’ the patient’s life to end. These results suggest that people’s use of the doing/allowing distinction depends in some way on their moral judgments.\
Highly recommended. If you are unfamiliar with the growing body of work in experimental philosophy, this is a nice paper with which to start.