Comparative Mythology: It's Uses and Errors

Since the rise in popularity of Karl Jung and Joseph Campbell there has been a movement toward an anthropological approach to mythological studies. This is both a good and bad thing.
In the good column, it's gone a long way toward helping mostly Western anthropologists in understanding other cultures. It's also helped to identify some commonality of experience in all cultures, so that a baseline of the range of human experience can be clearly understood. This gives researchers a handle on understanding a culture when studying it.
On the bad, it trivializes cultures and creates commonalities where they don't exist. It also places a modern paradigm on the whole study of a culture, and that culture may have perspectives differing far from the modern viewpoint. And of course it also tries to place things in a single box when that may not be applicable at all.
I've mentioned this before, but it merits mentioning again. In the tale of Phaedra from the Hellenes, Phaedra, the wife of Theseus, develops a crush on her step-son, Hypolatus. When he rebukes her, she, fearing for what her husband thinks, lies to Theseus and contrives to have her step-son killed, which happens as Poseidon sends a sea monster which spooks Hypolitas' horses, causing him to smash into a tree. (I may have misspelled a name or two in this -- don't have the time to look these up right now) To modern minds her infidelity and lying are her crimes. To the mind of Racine in the Age of Reason her crime is letting her passions overtake her reason. And to the ancient Hellene her crime is not paying proper respect to Aphrodite, who orchestrated her passions for her step-son in the first place, a crime that modern minds wouldn't even think about without being informed a bit about the culture.
Another problem with Comparative Mythology is that it's too easy to view all of the same type of story, god, or situation as archetypical and thereby lose the cultural significance of the situation. To consider the death of Balder as just another Dionysian tale of the god who rises, dies, and is reborn again robs the story of the powerful context in it. It doesn't address the haughty and egotistical Frig's failure to protect her child from all threats, it ignores the sacrifice Loki makes to give his wife's life meaning, (as a shapeshifter and a very clever individual, he needs nothing from his wife, so by allowing her the service of protecting him from the poison of the asp when, as a shapeshifter, he could easily get away, he gives her role as his wife meaning) and it trivializes the whole act of Balder's descent to the right hand of Hel and his eventual return after Ragnarok. This files the numbers off the myth, and reduces the cultural context to a pale echo of what it is in the culture.
Furthermore, it becomes easy to treat all trickster gods, for example, as a needed part of a culture as an outlet valve without looking at the individual cultural contexts involved. Loki is not Hermes. Hermes is not Ellegua. Ellegua is not Coyote. Each one has very clear differences that relate directly to the culture that spawned their legends, and there are subtle differences, and some differences that aren't so subtle. To compare Hermes, a god that was well respected by the people, and Loki, a god who the people looked upon as an abberation, and Ellegua, a demigod who people looked on as a needed figure who they had to be careful of lest his tricks come down upon their heads, as three similar gods is like comparing Tyra Banks, Janet Reno, and A female IRS tax auditor. And these differences are mostly steeped in the cultures that spawned these figures.
This is especially true for Norse practice. For most of the Scandinavian peoples, contrary to what many Asatru and Neo-Pagans/Neo-Heathens think, the gods weren't something the people wanted in their lives. They sacrificed to keep the gods OUT of their lives, because once the gods got involved, your freedom was compromised and all things would be for the glory of the god or goddess in question, not for the person's kin and kith. Examples from the literature clearly indicate that divination and calling on the gods was a measure of last resort, when things were so messed up that losing one's freedom was a small price to pay to keep total disaster from falling upon the heads of the group.The concept of a follower of one god or goddess to these people was a foreign concept, as that meant that only that deity would leave you alone. The gods were given their due, and then the people knew that they had a fair chance to live in peace for a while. This puts a strong cultural patina on these people, and differentiates them from those cultures where interaction with the gods was a contractual one. (You will provide us with good rain for the crops and I will sacrifice this goat) These kinds of cultural elements make it hard to compare the cultures of different peoples.
There's one more pitfall, one I consider to be the worst. When one gets to the point where all pantheons can be compared to others from a strictly scientific point of view, it has the potential to remove a lot of the power and magic from the pantheon. This makes it hard for such people to really find a spiritual center. It all becomes academic, and this not only is a strong disservice to the pantheons in question, it's a strong disservice to the person who is codifying them, because it divorces the person from the meaning and depth of the culture and path, and makes it difficult for any of them to resonate with their soul. It's like reducing Beethoven's fifth symphony to a series of numbers showing the mathematical relationships between the notes -- it becomes too clinical to reflect the true beauty inherent in the faith.
Don't get me wrong, I see some value in such things. But there is a limit as to how much one can reduce things before they lose all meaning.