John Perry of Stanford University recently said, "Original sin is the most factual contribution of Christianity." While this may or may not be true, certainly the idea of original sin is a concept that has caught the imagination of most Protestant believers. The basic idea is that every person is born with evil already in their genetic code. Some have more serious sins they are bound to do, but all have corruption in their bones.
The idea of total depravity is not just that sin exists in the soul of every person, but that every action that every person does is founded in base motives. This means that even a good action is done with evil motivation. In other words, a person who saves an infant from drowning may be doing it simply from the glory he or she might get from doing it and a mother sacrifices for her child because it is her progeny, her future existence on earth.
What the Bible actually says is that every person sins. It doesn't actually describe how this is so. It could be completely environmental-- that the fact we are raised in a sinful society that keeps sin going. It could be because of how we are raised. It could be that sinning is at first an accident that we find works. Personally, I lean toward the idea that our society connects with genetic factors which encourage us to act in evil ways, even when our thinking is right. Have you ever seen someone speak all the right words about helping and hope and love but still do things that harm others? This self-deception has to be learned, I think.
The total depravity concept is that we are born with self-deception. It is in every person's basic nature. This also means that no person can tell the truth. For if we are all self-deceived, how can we possibly tell the truth to another? How can we even tell any truth from a lie?
Total depravity seems like an unnecessarily negative viewpoint of human nature. Sure, all humans are sinful. We all screw up and we all hurt others on purpose on occasion. A few of us make a habit of it. But is the main characteristic of humanity sin and evil? Isn't it an equal part of humanity that we want to see our motives as good? Are we such complete failures as a species? Isn't it possible for us to improve? It says in Scripture about humanity, "They can do anything they set their hands to" Genesis 6. I agree that our track record is spotty at best, and that as a group we only can respond in the most Neanderthalian of ways. But we intend to do good. We may not know what the good is, but we try. That's not total depravity. Total stupidity, maybe.
BTW, The Human Centipede is shown simply because it was the most depraved movie I could think of.