At the risk of dragging this thread way OT:
For me to withold that knife, I must assert a greater moral capability than my friend. I am, in effect, making the moral choice for him. This is the same attitude that the Chinese goverment has when they ban certain websites on the grounds that the sites are seditious.
Again, I disagree. You are correct on the one hand if you say that it is not our place to make moral choices for other people. Aside from the fact that if you choose to live in a society that sets certain moral standards (you shall not kill, etc), some of which are even 'universal' standards that you will find wherever more than two people join together, you will have to live according to those standards, people should be able to set their own moral compass.
On the other hand, witholding our hypothetical murderer a knife does not equate to making a moral choice for him. He has already made his moral choice, you are just providing one means of acting upon that choice. In effect, you yourself are making a moral choice - you are choosing to believe that your actions in this case will not have harmful consequences, or rather, that whatever harmful consequences they will have are not your fault, and thus not your moral repsonsibility. That's where I disagree with you. I would withold the knife.
Perhaps, if you want to discuss this further, we should take this elsewhere - this is a Perl community after all, not a moral debating society :)