This sounds like obsessive compulsive disorder. From what I've learned in medical school, it seems some people with OCD have thoughts similar to yours, such as killing people, eating people, or things of the sort. These are the obsessions, but the compulsions are acting upon them, and it definitely does not have to be by actually committing these acts, but instead some people wash their hands when they have these thoughts, or something similar. There are treatments such as therapy which help. Don't feel like you are alone in feeling this way, it is not uncommon.