I don't think one can choose to be a psychopath, you either are one or you aren't. However, you are right in that empathy can often prevent people doing what's really best for people. An important thing to remember is, empathy only really works with people we can see/hear with out senses; suffering that is out of sight is usually out of mind, as they say. This is, in my opinion, the biggest reason we have such difficulty dealing with mental illness. It's much easier to empathize with someone who has a broken leg, compared to somebody who is depressed.