There's nothing artistic about moderating, nor is there any artistic talent needed.
And moderators are hardly ever chosen for the knowledge on topic in any type of forum.
Actually, despite (or because of?) being a qualified (Mathematical and Computer) scientist, I see there is definitely an art to moderating. Indeed, it requires a healthy dose of both art and science.
Any system dealing with people relies heavily on "humanities", or "social sciences" (although I do scoff at the usage of the term "science" there).
Computer programming is all about rules, you can generally predict precisely what a computer program will do in response to a set of rules (hardware or OS bugs notwithstanding).
However, when it comes to dealing with people, you can set as many rules as you like, but there will always be grey areas, interpretations, exceptions, biases. Navigating these grey areas is where the art comes into it.
Like most things in life, moderation is about balance. Moderate too hard and you stifle the community. Moderate too little and you allow destructive behaviours and characters to flourish.
It's not easy, and you can't always get it right. Personalities play a huge part in the tone and vibrancy of a forum community, and everyone is different.
I do try and apply a veneer of science to the moderation of the community here on Somersoft. We use the infraction system as a numeric count of the number of times someone has crossed the line - too many infractions sees a user get banned for a while (too many more and the ban is permanent). The problem is that there is still a subjective "art" to determining when to assign an infraction vs just removing the problem (ie editing or deleting offending posts) and letting things continue. Even a ban is not permanent - you can always register as a new user ... although we tend to be less forgiving with someone who re-registers after being banned, but there have been some people who become model forum citizens after being banned.
You just need to look at the feedback the moderation team get to see the challenges faced in getting the balance right. The same issue will see both praise and condemnation from the community. Some people think we are too harsh, others think we are not harsh enough. Some people think we should ban some individuals for lowering the tone of the forum, while others think we should leave them alone because they add colour to the community. It's often a case of damned-if-you-do and damned-if-you-don't when it comes to moderation.
There is no easy answer to some of these questions, but that is also why we have a team of moderators - we bounce questions about moderation off each other daily. Other than simple cases of spam, almost all reported posts get several replies discussing how we should approach an issue. It is also useful to have a largely detached "owner" in Ian Somers who can act as a fairly independent arbitrator, since he typically has no personal history with any of the people affected by moderation decisions.
Finally, I am a strong believer in never making permanent changes in the course of moderation. That means making sure that whatever action is taken, that it is largely transparent, and can always be undone or reversed. I do lift bans, I do undo deletions and I do withdraw infractions where I think (or have been convinced) that we overstepped the mark, or decide to give people another chance.
Most things in life are rarely black and white.