In 1954 Congress, led by Dr. Fredrick Wortham in particular (author of the book Seduction of the Innocent), decided that horror comics were warping the minds of the nation's youth, and called special hearings to look into the matter. Publishers, artists, writers, politicians, doctors and more were called before the Senate in 1954 for the Senate Subcommittee Hearings into Juvenile Delinquency, with the special focus on Comic Books.
You can read the entire transcript at this website:
This is a 300+ page document that was posted on the internet by Jamie Coville. It's fascinating reading - There are links to the individual sections of the hearings, so you can, for instance, jump right to EC comics publisher William Gaines testimony. There are also color reproductions of the comic covers that were presented to the Senate.
As a result of all of this the comics industry was forced to adopt a comics code. Without it, no comics could be published. It's all pretty unbelievable nowadays, but they were serious with these restrictions, and for years the comics industry had its hands tied by this code.
Here's the part I found most interesting in the comics code, as it deals directly with horror in comics. There was of course much more to the code, dealing with religion, profanity, attire of characters, and marriage and sex. Note the part about no vampires, ghouls, cannibals, or werewolves. Guess they felt that encompassed the totality of monsterdom. General Standards - Part B
General Standards - Part B
No comic magazine shall use the word "horror" or "terror" in its title.
All scenes of horror, excessive bloodshed, gory or gruesome crimes, depravity, lust, sadism, masochism shall not be permitted.
All lurid, unsavory, gruesome illustrations shall be eliminated.
Inclusion of stories dealing with evil shall be used or or shall be published only where the intent is to illustrate a moral issue and in no case shall evil be presented alluringly nor so as to injure the sensibilities of the reader.
Scenes dealing with, or instruments associated with walking dead, torture vampires and vampirism, ghouls, cannibalism, and werewolfism are prohibited.