Most religions tell people that they should try to suppress thoughts of doing evil things, but mostly only the Catholics claim that the actual thought is the sin and must be atoned for. This can be traced back to the Church's embrace of Plato's theory of an actual World of Ideas, and that the world we live in is only a poor reflection of this world.
Actually, for many people, some sort of activity (punching bags, whacking golf balls, writing descriptions) is a good way to dispel hostile thoughts. Freudian psychology uses reliving difficult moments in the imagination as an effective way of removing recurring obsessions permanently. Confession, which is a lot simpler and less effective, is the RC Church's only method, and is less effective.