Hawthorne, along with Poe and Melville, made up a group of American writers known as The Dark Romantics who wrote during the same time as Emerson and Thoreau, the two primary Transcendentalist authors. The two groups of writers had vastly different views of mankind's nature, and that is why many would classify Hawthorne and Poe as being opposed to Transcendentalism. For example, both Hawthorne's and Poe's works feature characters (especially narrators in Poe's case) who have succumbed to their inherently evil nature. Hawthorne's short stories "The Birthmark" and "Rappaccini's Daughter" are evidence of his pessimistic perspective of man's soul. Similarly, Poe's stories almost always include a narrator who is overcome by rage and greed ("The Tell-Tale Heart"), an addiction to alcohol ("The Black Cat"), revenge ("The Cask of Amontialldo) or other "sins." Both authors do not write these stories as exceptions of man's potential for evil but rather as what they view man's nature to be.
In contrast, the Transcendentalists propose that no limits exist when it comes to man's potential for good. According to Emerson's "Self-Reliance," man can become an independent thinker who eventually cannot be influenced by the conformity (or evils) of society. Similarly, Thoreau promotes individualism and civil disobedience because he perceives man as an optimistic being who has the power to do great good.
While many of Hawthorne's and Poe's characters are separated from society and struggle with morality, very few of those characters can blame their poor choices on society's influence--rather, they have removed themselves from society, and their evil natures take over (according to the Dark Romantic point of view). In contrast, the Transcendentalists illustrate in their writings the importance of man separating himself from society (going into the solitude of nature for example) to find the inherent good in themselves. These are two completely different perspectives of mankind.
Interestingly, Hawthorne and Emerson were good friends. Hawthorne even tried living in Emerson's utopian community for a while, but rather than uplifting his view of man, the experience left Hawthorne disillusioned with his fellowman. He found that few who were part of the commune really wanted to work or be a contributing part of a community.