"Your opinion of it is very just. The subject is by far too horrible, and I confess that I hesitated in sending it especially as a specimen of my capabilities... But what I wish to say relates to the character of your Magazine more than to any articles I may offer... The history of all Magazines shows plainly that those which have attained celebrity were indebted for it to articles similar in nature—to Berenice... You ask me in what does this nature consist? In the ludicrous heightened into the grotesque: the fearful coloured into the horrible: the witty exaggerated into the burlesque: the singular wrought out into the strange and mystical. You may say all this is bad taste. I have my doubts about it... But whether the articles of which I speak are, or are not in bad taste is little to the purpose. To be appreciated you must be read, and these things are invariably sought after with avidity. They are, if you will take notice, the articles which find their way into other periodicals, and into the papers, and in this manner, taking hold upon the public mind they augment the reputation of the source where they originated."Poe concludes that he admits "Berenice," in fact, "approaches the very verge of bad taste—but I will not sin quite so egregiously again." He notes that similar stories are coming, but he asks White not to judge them without first considering their impact on the circulation of the magazine.
"Berenice" was Poe's first true horror story. In later editions, Poe did self-censor a tiny bit (it's hardly noticeable) but he didn't really back down in the theory he discussed in the above letter to White. He purposely tried to bring his stories right to the edge of grotesqueness, but still keep them entertaining. This letter allows us to question the sincerity of his horror stories and if he really believed they were worthwhile literature. This "pop culture" approach justifies his decision to use themes like premature burial, mesmerism, and other subjects which audiences gobbled up. Of course, Poe presented these themes very differently than most; as mentioned above, gratuitous violence was replaced with suspense and underpinnings focused on the narrator's psyche.
Either way, to me, this shows that Poe knew the publishing industry and, most importantly, he knew his audience. His line about being read in order to be appreciated refers just as much to White as himself; he was holding a carrot in front of White's nose to let him know he intended to increase the magazine's circulation - for White's benefit. And, from what we can tell, he succeeded.
Of course, Poe wasn't entirely sincere about never sinning quite so "egregiously" again. And White knew that. White seems to have had a decent relationship with Poe in his early career and tried to support him through a difficult time. Poe biographer Kenneth Silverman suggests a "fatherly" interest. It's also possible that Poe pursued White's daughter Eliza, then 18, as a potential wife (about a year later, Poe married his young cousin Virginia instead).
*The image above is a screenshot from an amateur film adaptation of "Berenice," created for a graduate film course. The full video (before a custom soundtrack was added) is here.