*Please read the whole thing before criticizing; it all glues together. *I took the word definitions from online sites.
Psychological types are not inherent for all (i.e. are not purely genetic and given at birth) because human interpretation and understanding is too variable in its capacity to change and adapt to environmental stimuli. Personality is grown through various encouraging and discouraging aspects of the environment, which includes the direct effect of other human beings in communication and the direct effect of human force between human beings, as well as certain genetic characteristics a person may have. Types can only be applied to past timelines of a person's life and does not have to remain a constant. So the functions do exist and can be used to determine what types of judgements or information perceiving a person is doing in a given historical context and even apply types at various intervals. But to assume a current type is to propose to act as that type into the future (since the future is now), and is only such.
A. Consider something such as physics and mathematics. Newton came up with basic theories that were able to merge mathematics to create laws and an understanding of basic physical characteristics that we witness in the world around us, such as F=MA. We can throw a ball and understand that it will come back down to us and use math to see how this will occur with time. Because of this we can apply this law to many things to create machines that will obey these laws and make our lives easier or more enjoyable. And because of that there are very few who (probably mostly consisting of religious zealots) would dare to obstinately and ardently crusade that these laws do not exist (above the quantum level). It's possible understanding the quantum level of what is going on could lead to an alternate understanding and use of how to manipulate things above the quantum level, but regardless of that, the physics laws we have have stood the test of time and are collectively agreed to exist and validly explain our physical world with a specific understanding of not what goes on in the quantum level of matter and the universe. In conclusion, physics (above the quantum level) is seen as the objective understanding of inanimate objects, where inanimate means that the objects do not share the intelligence applied to a life-form (where life means the condition that distinguishes organisms from inorganic objects and dead organisms, being manifested by growth through metabolism, reproduction, and the power of adaptation to environment through changes originating internally.). From this we can say that since inanimate objects do not share any of the characteristics of a life-form to adapt to an environment that the inanimate object is opposite to a life-form and therefore lacks intelligence since it is subject to the understood and certain objective laws of physics around us (above the quantum level).
B. Consider something such as intelligence. If we say that intelligence is the capacity for learning, reasoning, understanding, and similar forms of mental activity; aptitude in grasping truths, relationships, facts, meanings, etc, then we can say that a life-form has to have intelligence to fulfill its definition of being able to adapt. Then if we consider that inanimate objects (essentially everything else from a life-form) do not adapt (as explained in section A) then they do not have intelligence. Thus we can say that to understand a human being, or any other life-form for that matter, we can not talk about that life-form's intelligence without also talking about the environment that it struggles and adapts to. In this way, a life-form's intelligence is described and explained through its past interaction with its environment, in a historical sense. And to accurately compare the intelligence of two different life-form's one must observe them in exactly similar environments, or the comparisons are invalid. So how can we explain the differences in intelligence between two life-forms when they have exactly the same environments? Genetics.
C. It can be said that to be a life form one must be capable of adapting to at least one environment to survive, since that is part of the definition of life we are using here. So we have the human ability to adapt to an environment through the use of a conscious intelligence that attempts to understand its environment as best it can and adapt to it. Part of that adaptation will be a result of genetics. These genetics could lead to one person understanding emotionally expressive interactions with people better than most others. Other genetics could give someone better reflexes or strength or even a photographic memory. Genetics is obviously going to be important in a person's intelligence and some people will have better talents than others as a result. But nonetheless one still has to interact with the environment to learn about and utilize the talents they have. If they aren't utilized, then they won't be apparent in a person's intelligence. And inversely, if they are utilized, they can be apparent in a person's intelligence, but may not; this is because some talents could be seen by society or maybe even the person as useless and will be suppressed or limited and not a main or easily apparent focus of a person's intelligence.
D. What does personality have to do with intelligence? If intelligence is what describes and explains life-forms, then personality must be a frame-of-reference of a human life-form's intelligence. Thus personality is shaped by environment, as much as it is by genetics.
Conclusion: Personality-Type can only be used to explain a person's historical behavior, and since it is dependent upon environment, it is not appropriate to suggest type as given at birth, or something set-in-stone; and to assume a type is then to propose a resolution (unconsciously or consciously) to be that type into the future.
*I've been needing to get this out for a long damn time. I hope someone actually understands this.