Beorn was, like many of Tolkien's characters, of somewhat mysterious origin and also clearly was not totally described or explicated.  As you said, he is generally a character in the light category as he is mistrustful of strangers but otherwise friendly to the "good" guys, and has taken on many of the dark enemies in the past as well as during the hobbit when he takes on and kills the Goblin king.  His bond with animals both his trained animals and others in the wilds is very strong and he demonstrates a respect for animals we think of as non-sentient and recognizes that they have talents and are special and unique.  Despite being able to shift into bear shape, he did not eat meat and demonstrated further respect for animals in this way as well.