I want to further classify INFJs and possibly all NFs.
The 2 most glaring categories I can think of would be:
False Idealists - Idealism
True Idealists - Realism
Idealism to the max, you would rather destroy all just to prove your point of idealism. These types of INFJs/NF's will often forcefully defend ridiculous and absurd ideas that are ideal in nature, but do not work so well in reality because not everyone thinks the same. Usually young and naive, this is an NF who hasn't actually had much experience in dealing with the real world or who has lived a more comfortable life in general. They claim to be idealists, but their narrow vision of reality and their tenacious grip on their unflinching emotionally based idealism makes them more harmful than good because they will inevitably end up trampling someone elses freedom in order to push their views.
Idealism within logical reason. This is a person who sees an ideal and then strives and works towards it in a more ethical way. This person will usually understand that an ideal may not be possible, but we can get closer than we are, an so goes to effect that true positive change within the framework of our society's system. Instead of ignoring that not everyone can agree, the true idealist will offer solutions that include concessions for opposing view points. Because they are more realistic in this fashion they will effect more positive change over time than a false idealist ever can. This in essence will improve lives of people for real and not just in theory. True idealists deal with reality 1st then bring their creative talents to the table. This is a person who has likely tasted reality and knows both triumph and defeat. More than likely has lived a life that has had periods of intense pain and suffering and as such knows what true penalties can lay in wait for a person just short of death. This kind of INFJ/NF knows the boundaries of reality and works to ensure their vision is fulfilled as fully as possible within those limits.