Q: Is Sarcasm Immoral? A: Any idiot knows it's not.
I've heard people make this claim: "Sarcasm always has a victim" I'm not so sure that's a proper analysis.
Although, sarcasm always introduces pain (i.e. mental pain) unto someone (which is the point of using it), that is not sufficient to make them a victim. Negative reinforcement can be a positive learning experience. Sarcasm is a particular type of negative reinforement; thus, sarcasm can be a positive learning experience.
For instance, Socrates used sarcasm to shock individual people into thinking and as a device for improving the quality of the whole community (by improving its leadership and educators). And other great moral figures have also used it to good effect. Take, for instance, Jesus' approach when the Pharasees would not listen to his more measured lessons. In fact, Jesus was really good at it.  Matthew 3:7 -- But when he saw many of the Pharisees and Sadducees coming to where he was baptizing, he said to them: "You brood of vipers!  Matthew 12:34 - You brood of vipers, how can you who are evil say anything good? For out of the overflow of the heart the mouth speaks.  After the telling of the parable of the tenants in Luke 20, The teachers of the law and the chief priests looked for a way to arrest Jesus immediately, because they knew he had spoken this extended parable against them as a sarcastic ploy.
A related issue is the difference between satire and sarcasm. I don't think there is any, since one's person's joke is another person's affront. It just depends on which side you're on.
So, in the end, sarcasm does not necessarily victimize. It might, but it need not. It depends on the intention of the agent behind it's use.