I said in a previous blog that I felt art is defined by the way it is limited by the imagination, while a craft is defined as something limited by its medium. By this standard, informal logic (argumentation) can be either a craft or an art, depending on how the arguer pursues it.
If one conforms to some standard of logic - ie. consistency, avoiding logical fallacies, logos/pathos/ethos - then I'd tend to say that arguing is a craft. If you
either pay no attention to such limitations or only use them when they're convenient, I'd say argumentation becomes an art form - the ideas/arguments you present are limited only by
your imagination. And obviously I'm not saying that's a positive thing; perhaps 'artistic' shouldn't necessarily carry a positive connotation.
If we take as an example 9/11 and the illnesses reported by ground zero workers (Mesothelioma due to Asbestos exposure), we see argumentation as a craft and as an art. As a craft because there are those who point to the facts and argue accordingly ("The government knew the air quality was bad at Ground Zero and covered it up because they wanted to keep Wall Street running; here are the reports and testimonials to prove it") and those who argue more 'artistically' ("That's not true, because the government wouldn't put money ahead of people's safety "). Argumentation as a craft is helpful and closest to the truth, argumentation as an artform becomes hurtful and serves vested interests instead of the truth.
I think this is primarily where lawyers get a bad rap - our tendency to view their arguments as clever sidestepping rather than solid reasoning, as Artists rather than Craftsmen. Should McDonald's get sued because they didn't warn that old lady not to keep the hot coffee between her knees while she was driving? An attorney will make you (of if not you, a lot of other people) think so. Or on the flip side, a lawyer for McDonald's could argue that the restaurant chain shouldn't be held to any standard of public safety, because it's got a moral duty to its stockholders to maximize profits and safety precautions hurt profits (intelligent people on BOTH sides of an issue can be full of shit).