It does sound like you may be suffering with OCD - having intrusive thoughts about hurting people (or animals) is a very common type of obsessions in OCD - but, unlike psychopaths, OCD sufferers do not take pleasure in these thoughts but are horrified and scared of them (which seems to be the case for you) - and never act on these thoughts, they are just very anxious that they "might" act on them. One of the most effective ways to deal with these thoughts is to stop attaching great significance to them and to stop fighting them (suppressing or fighting intrusive thoughts tends to make them worse) - most people get weird thoughts (including those of violent nature) from time to time, but by paying too much attention to them that we may be putting ourselves at risk of developing an anixety disorder.
Having these thoughts does NOT mean that you actually want to do it and does NOT mean that you are a bad person - it just means that you are a sensitive person and are scared of causing harm to others.
Below are some links to organisations that offer support and information about OCD.
Stuck in a Doorway - Online OCD Forum
The Royal College of Psychiatrists' Leaflet on OCD: http://www.rcpsych.ac.uk/mentalhealt...edisorder.aspx
Treat It, Don't Repeat It: Break Free from OCD