Had Hawthorne been of the same generation as William Golding, he would have been in accord with Simon who realizes that the "beast" is within the boys, inherent in the nature of man. This knowledge of innate evil, Young Goodman Brown misses; consequently, he rejects Faith when she greets him. While his knowledge is ambiguous, "a black cloud of doubt" covers him, he does, however, realize that his Puritan Calvinistic faith is more diabolic than divine. It is this disillusionment in Calvinism that causes Brown to learn the full terrible significance and irrelevance of his Puritan faith with its simplistic division of the "elect" and those predestined to condemnation. There is "misery unutterable" for Brown because he has come vis-a-vis with his own evil. Indeed, it is this recognition of evil in the very hearts of men that causes Kurtz of Joseph Conrad's The Heart of Darkness to exclaim despairingly, "The horror! the horror!" For, evil is no force outside himself in the world; instead, it lies within the man himself.
According to Henry James, an admirer of Nathaniel Hawthorne, the emphasis on human wickedness in Hawthorne's work was not to be taken too seriously. Hawthorne was using it for artistic purposes. What happens to Young Goodman Brown and his sweet little wife in the story is somewhat shocking, but it is also intended to be somewhat amusing. Hawthorne did not believe "that there is a powerful force of evil in the world, actively working to bring horror and destruction," to quote your question. He was too intelligent and too well educated to hold such superstitious beliefs. He did believe that there are bad traits in all humans which most of us take pains to conceal, perhaps even to conceal from ourselves. Hawthorne's stories about human evil, like Poe's, should be taken with a grain of salt. It is true that some people do bad things, but not that they are being controlled by the Devil. Such notions were common among the Puritans, and Hawthorne was practically satirizing them in some of his tales. Readers find such stories exciting. Murder mysteries are the most popular genre fiction today.
In my opinion, I do believe there is a power of darkness and evil in the world. Of course Hawthorne personifies this evil in the man that Brown meets on his travels through the forest. And he alludes to the involvement of evil in the lives of even the most upright, as those who he sees in the woods have their own personal relationship with this personification of evil, as did (Brown learns) his seemingly upright ancestors.
For me, I only need to look at men like Hitler or Charles Manson. (And there are so many others.) I turn on the news and see it every day. Someone might suggest that these are sociopaths, people who feel no guilt for what they do. However, I believe that except for those who do not know the difference between right and wrong because of a mental condition (as opposed to those who know, but ignore this distinction), the horror other human beings are subjected to at the hands of evil people convinces me that evil is "alive and well" in the world. Most recently is the case of Jerry Sandusky. It breaks my heart to think of the young boys he has terrorized and abused. How can there be no evil in the world when our children are no longer safe? When life is cheap and the taking of it, as in Darfur, is a casual event that does not even seem to cause hesitation, however brief?
The story of Young Goodman Brown is allegorical, and as such, I believe it touches on the truth of what Brown faces in Hawthorne's view of everyday life. As is the case with those who practice evil in the world, one has a choice as to how he or she reacts to it. Brown becomes a miserable old man who chooses to mistrust everyone rather than fight for goodness and find the light that exists in people who choose to battle against the call of sin. For theologically, all live in sin. It is what one chooses to do in light of this that separates the Browns from the Faiths.
In terms of Hawthorne's view, his work is appreciated because...
....[of] its storytelling qualities and for the moral and theological questions it raises.
Certainly Hawthorne must have believed in evil, for the actions of his own ancestors. One was a magistrate...
...who once ordered the public whipping of a Quaker woman.
Another was guilty of condemning the innocent to death during the Salem witch trials of the 17th Century in Massachusetts.
To me, evil has its own way with Brown—for his sin of pride and his judgment of others (both in opposition to the Christian teachings, but so embraced by the Puritans, of which Brown was one) turn him into someone who is filled with darkness and is unable to live charitably with others.
It was a dream of evil omen for young Goodman Brown. A stern, a sad, a darkly meditative, a distrustful, if not a desperate man did he become from the night of that fearful dream. On the Sabbath day, when the congregation were singing a holy Psalm, he could not listen because an anthem of sin rushed loudly upon his ear and drowned all the blessed strain.
Yes, I believe there is a "force of evil in the world, actively working to bring horror and destruction." Its tools are people, only too willing to do what they want without regard for others.