How do I get rid of unwanted thoughts of harming others?

It sounds as if you are feeling extremely distressed by these thoughts and impulses, which is actually a good sign that you are not going to act on them.  If the thought of harming someone was pleasurable for you, it would be more of a concern!  But the fact that you are feeling so distressed and are in fact instigating avoidance behaviours by getting away from the object of the thought because you’re feeling scared you will actually carry out the aggressive action tells me that you are suffering from an anxiety rather than a macabre change in personality.  It sounds as if your anxiety is double-edged – you are already anxious, which is generating the obsessive thoughts, and you are also anxious you will carry out the behaviour in your thoughts, and therefore doing avoidance behaviours.  Anxiety begets anxiety, and avoidance behaviours reinforce obsessions, and that is why you feel as if it is getting worse.  Obsessive thoughts are often part of a disorder called Obsessive Compulsive Disorder (OCD), which is characterized by obsessions and compulsions.  Obsessions are disturbing thoughts, images, or impulses that increase feelings of anxiety. Compulsions, or rituals, are the strategies that individuals with OCD use to reduce the anxiety associated with obsessions.   It’s important that you find a therapist who is experienced in working with people who suffer from OCD as there are specific therapies that have been found to be successful for this.  Once you begin to do the work required in therapy to short-circuit the “loop” your thoughts are running in, you will find the relief you so desire and need.