I suggest you read through EYs ethics posts, they provide an interesting answer to this question (if you already have read them then I apologise).
Literally to the question "How repugnant a thing should you be willing to do...?" If you gave me a link I would be grateful.
Joshua Greene manages to squeeze his ideas about 'point and shoot morality vs. manual mode morality' into just 10 minutes. For those unfamiliar, his work is a neuroscientific approach to recommending that we shut up and multiply.
Greene's 10-minute video lecture.