Intuitively, imposing a game of Russian roulette on an innocent victim is constitutive of twice as much moral depravity when there are two bullets in the six-shooter as when there is only one. If so, then a one-bullet game of Russian roulette will carry about a sixth of the moral depravity of a six-bullet game, and hence about a sixth of the depravity of plain murder.
I am not so sure, though. The person imposing the game of Russian roulette is, I shall suppose, intending a conditional:
- If the bullet ends up in the barrel, the victim will die.
- If you can't pay the mayor off, get rid of him.
Perhaps, though, this judgment about the moral depravity of issuing order (2) is based on the thought that the kind of person who issues this order doesn't care much if the probability of integrity is 0.001 or 0.1 or 1. But the person who intends (1) may well care about the probability that the bullet ends up in the barrel. So perhaps the mob boss response doesn't quite do the job.
Here's another thought. It is gravely wrong to play Russian roulette with a single-bullet and a revolver with six thousand chambers. It doesn't seem that the moral depravity of this is a thousandth of the moral depravity of "standard" Russian roulette. And it sure doesn't sound like the moral depravity goes down by a factor of ten as the number of chambers goes up by a factor of ten.
Here, then, is an alternate suggestion. The person playing Russian roulette, like the mob boss, sets her heart on the death of an innocent person under certain circumstances. This setting of one's heart on someone's death is constitutive of a grave moral depravity, regardless of how likely the circumstances are. It could even be that this is wrong even when I know the circumstances won't obtain. For instance, it would be morally depraved to set one's heart on killing the Tooth Fairy if she turns out to exist, even when one knows that she doesn't exist. There is then an additional dollop of depravity proportional to the subjective probability that the circumstances obtain. That additional dollop comes from the risk one takes that someone will die and the risk one takes that one will become an actual murder. As a result, very roughly (in the end, the numerical evaluations are very much a toy model), the moral depravity in willing a conditional like (1) and (2) is something like:
- A + pB