Our college chaplain used to preach often against sarcasm. This always baffled me, and made me assume that the poor fellow, though clearly holy, was a little bit clueless. After all, a stroll through the nearby woods would show him that the students in his care were engaging in much worse sins than a little snarkiness!
Now I think two things: (a) of course he knew what was going on in the woods; and (b) he was onto something. Sarcasm is the younger, rather juvenile sister of irony. Irony is wonderful as a literary vehicle -- but as a lifestyle, it's deadly. A habitually ironic point of view trains us to see the world at a distance, to never approach our consciences directly.