My personal theory is that if we allow that people can change it means that we have no excuse for our own bad behavior.
Now granted barring a head injury or a profound religious experience I have never seen someone drastically change but it is possible. So the flaws in my own character are there because I lack the discipline and will to change them. I am not sure I care for that but what is, is.
obviously you have never spent time in the "recovery community" (AA etc.). People don't stay in recovery from their addictions unless they give up the dysfuntional behaviors that helped lead them their in the first place........