I began my study of Comics Censorship without knowing much about it, that is, without having my mind made up in advance. What I found is that there isn’t a tremendous amount of historical writing on the subject. there is considerable legal writing, and the comic books legal defense fund’s records were an invaluable resource, but they’re firmly on one side of the issue, and not given to cutting their opponents much slack, for perfectly understandable reasons. The result, is the available data is slanted against the censors (and i’m already predisposed to dislike anyone who goes by that descriptor). What I was able to learn was, in broad strokes, follows.
Comics have been treated as “something dirty” for the best part of a century, and only recently have started to be recognized as a legitimate art form that can be enjoyed by adults as well as children, and this is mostly due to life-long readers aging into positions of authority and prestige in the publishing and criticism communities, rather than any great awakening on society’s part. No occasion in Comics history raised more vitriol (without ending in the offending book’s immolation) than TIME placing Watchmen on it’s “100 Greatest Novels List”, but that didn’t happen until 1999 (while Watchmen was originally released as 12 a 12-part limited series, it was released in 1987 and 1995 as a single volume, and a post-Cold War American Public was less sanguine about the burning of bound texts.
Early in comics history, the stories and images depicted were firmly adult, and the sub-genres, comic horror, comic sci-fi, and comic crime, even more so. They were, nevertheless forms of protected speech, that, because of their apparently childish appearance, were denied said protection and were burned with impunity in public spaces.
In order to avoid federal interference in their industry, the comics publishers formed the Comics Code Authority, an example of an industry regulating itself, in some cases much more firmly than the federal government might have. The CCA didn’t have prior restraint authority, but the distributors knew the score, and wouldn’t buy comics that hadn’t received the CCA’s seal of approval. The Comics Code Authority imposed the following regulations, please bear in mind this isn’t a complete list.

Crimes shall never be presented in such a way as to create sympathy for the criminal, to promote distrust of the forces of law and justice, or to inspire others with a desire to imitate criminals.
If crime is depicted it shall be as a sordid and unpleasant activity.
Policemen, judges, government officials, and respected institutions shall never be presented in such a way as to create disrespect for established authority.
Criminals shall not be presented so as to be rendered glamorous or to occupy a position which creates a desire for emulation.
In every instance good shall triumph over evil and the criminal punished for his misdeeds.
Scenes of excessive violence shall be prohibited. Scenes of brutal torture, excessive and unnecessary knife and gunplay, physical agony, gory and gruesome crime shall be eliminated.
No comic magazine shall use the words “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 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.
Profanity, obscenity, smut, vulgarity, or words or symbols which have acquired undesirable meanings are forbidden.
Nudity in any form is prohibited, as is indecent or undue exposure.
Suggestive and salacious illustration or suggestive posture is unacceptable.
Females shall be drawn realistically without exaggeration of any physical qualities.
Illicit sex relations are neither to be hinted at nor portrayed. Rape scenes as well as sexual abnormalities are unacceptable.
Seduction and rape shall never be shown or suggested.
Sex perversion or any inference to same is strictly forbidden.
Nudity with meretricious purpose and salacious postures shall not be permitted in the advertising of any product; clothed figures shall never be presented in such a way as to be offensive or contrary to good taste or morals.

As time (and the 1960’s counterculture) went on, the underground comics movement successfully undermined the CCA, and in 2011, the CBLDF acquired the intellectual property rights the the CCA’s seal of approval, formalizing the CCA’s slide into impotence (advertizers stopped caring in the mid-’90s), and ending the its authority for good.
Comic Books are the only industry of which I am aware that have any history of successful self-regulation. Regulation, that is, until market forces push out the regulators, but the History of comic books prove that while self-censorship is possible, it’s never pretty.