The Brawner rule states that:
"A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity to appreciate the wrongfulness of his conduct or to conform his conduct to the requirements of the law."
Anyone could clearly see that the Milwaukee Monster had the mental capacity to have killed and raped that many people... According to an article published on "The New York Times" , Dahmer "Had taught himself to live behind a mask of normalcy that hid his often contradictory emotions.".
So yes, Dahmer had emotional problems -- but not ones that left him mentally inept. Therefore, he was completely sane when he committed these grisly acts.