Cowardice is never a good reason to avoid a project, however.
A series proposes its own theory of good vs evil and needs to be consistent about it.
In any kind of fantasy, the inclusion of the supernatural automatically forces a series to have its own cosmology. Good and evil are often personified literally. One doesn't have to have a simplistic or traditional idea of what defines good and evil for this to be true. It applies equally to a devout Christian like C.S. Lewis, an atheist like Phillip Pullman or a Taoist like Ursula Le Guin.
Second world fantasy (where you create your own world, perhaps even with its own deities), is that it is more comfortably removed from discussing people's actual religions. Urban fantasy is a bit of a puzzle to me, because on one level it's the "real world" so obviously one is going to have Baptists and Catholics and Jews and Muslims, but on the other hand, I don't particularly want to take a proselytizing stand and advocate one over the other.
This is even more awkward because my topic is holidays, which are ... holy days. And not everyone in the world celebrates the same holy days. Obviously, it's not possible to write about holiday magic without addressing this.
Children's story about Jack Frost (like the Rise of the Guardians) or Rudolph the Rednose Rainbow or Jack the Pumpkin King evade this by dealing with the holidays at the level of children. Teasing is bad; sharing is good. I would like to go a little deeper than that.
As a writer, I am consistently enthralled by philosophical questions and by worldbuilding, and so I enjoy building worlds where I can explore philosophical questions. I try to keep this from becoming too heavy or preachy in the book itself. I hope that readers who want only a fast-paced adventurous and fun story will find that, and readers who are interested in other layers in the story will find that too.
I looked over a number of Urban Fantasy and Paranormal Romance books in my collection for some ideas about the struggle between "Good" and "Evil" is organized. Here are options I've seen:
Cosmic OrderExample: Touched By An Angel, Saving Grace, Quantum Leap, Lord of the Rings, Ghosthuntress, Chronicles of Narnia, Left Behind ...
All stories that are consciously Christian have a traditional cosmic order in which Good can / will / does triumph over Evil; even though it should be noted that not all stories in which Good can / will / does triumph over Evil are necessarily Christian. Lord of the Rings, for example is less obviously Christian in its mythos than the Narnia Chronicles, although Tolkien himself was a devout Christian.
Quantum Leap, for instance, is not explicitly religious, never mind Christian. The series is specifically vague about what higher power guides Sam's leaps into places where he can improve people's lives for the better. Late in the series, Sam meets another Leaper who appears to be working for an Evil power, although, again, details are deliberate left hazy.
Cosmic BureaucracyExamples: Good Omens, Dresden Files, Succubus Blues, Charmed, On a Pale Horse, Hunger, Insomnia ...
Both Good and Evil are organized like governments, or perhaps corporations, and the characters, whether nominally Good or Evil, work for them, as if it were a career. This is used in many books where angels and demons are characters. Good is still good, at least nominally, versus evil. However, compared to the traditional Cosmic Order model, there is more ambiguity about whether Good will or even should triumph over evil.
As it says on TV tropes:
Basically, Good and Evil are unionized, and have rules they must follow. These rules are usually towards overall self-preservation; no one side is allowed to "win" too much, and the Big Good and Big Bad restrict their fighting to a Divine Chessboard rather than going at it in person.
Local BureaucracyExamples: Buffy the Vampire Slayer, Wicked Lovely, Twilight, Anna Dressed in Blood, Being Human ...
There is a local or immediate bureaucracy, such as the Watcher's Council for the Vampire Slayer in the Buffyverse, or the Faery Courts. This is used in many urban fae, vampire and werewolf scenarios. The Even the good guy Local Bureaucracy is often as much a source of trouble to the protagonist as the baddies, without actually slipping into full role reversal.
The Local Bureaucracy often works in the context of a less clearly defined Cosmic justice system, which may include hell and heaven and other dimensions. Rules govern the larger cosmic system, but the characters don't directly enforce those rules.
Reverse RolesExamples: Queen of Orcs, Shrek, Wicked, Villains By Necessity, His Dark Materials ...
In the role reversed universe, what we were told were evil creatures are on the Good side and the traditional heroes are cast as villains. In Queen of the Orcs, orcs are a noble, abused race while most humans are scum.
Phillip Pullman, according to rumor, created his series as a protest against overly obvious religious symbolism in fantasy (cough Narnia cough) and so in his series, the religious fanatics are the baddies.
Even in a series in which Good and Evil are more or less traditional, a common modern trope has become the "the villains in White," modeled on Spanish Inquisition types. You don't have to have a full reverse role story to think that torturing and burning hundreds of people is a bad thing.
Note that in these scenarios, Good and Evil are still quite clearly defined, simply relabeled.
AnarchistExamples: Bloodsucking Fiends ...
Supernatural creatures simply wander around, clueless as to their higher purpose. Their behavior may also defy easy categorization. This category is often humorous.
Please feel free to list others examples or options....