It has been specificaly mentioned many times in the manga that the tailed beasts are not just a mass of chakra, but also hatred. I wondered why exactly hatred and not something else, like joy or lonelyness or any other emotion. Well anyway, thats when I came up with a theory that sounds quite good, to me anyway
In Narutoverse, it was many years before the current events that Juubi and the Jitsu Monk known as Rikudou Sennin were alive. We do not know how Juubi came to life, but what we do know is that Rikudou found a way to harvest its power by a human and thus the Jinchuuriki seals were created and not long after that Rikudou was forced to split Juubi into an empty body and 9 pieces of chakra.
Here I would like to add something about chakras. They are obviously the source of power, but they also represent a special identity. Example, Narutos chakra compared to Sasukes. One was described as warm, comforting and very light chakra while the other was the opposite cold heartless and filled with murderous intent. This just shows that emotional inner state is a factor that can change even the form chakra.
Now lets go back to Jinchurikies. I think it would be very logical to assume that humans, as they are greedy and evil, started to hunt down tailed beasts after Rikudou died to make use of theyre chakras in combat. Many tried, many fell sacrifice and only very few actually accomplished to control theyre beasts a little.
The core of my theory
This is where my theory starts. The only way for a Jinchuriki to gain proper control over the beast is just like Naruto showed us, they must pull theyre chakra out but at the same time the beast is pulling the users chakra for itself so it is a two-way channel of chakra. My theory is that right after the beasts were created, theyre chakras were pure and hate-free.
However, things started to change over the years bcs many ninjas were in need of power, they were made a Jinchurikies and after many centuries they managed to pass theyre hatred bit by bit, onto the beasts until the beasts became violent and extremely hard to subdue. Thats bcs as I stated before, using tailed beasts chakras also makes the beast to use some portion of users chakra. This was shown in the latest chapter where Kyuubi restored himself bcs Naruto used its chakra too much.
Take a quick look at the chapters where Naruto was fighting Kyuubi over its chakra. His first attempt to pull its chakra was almost a failure. Kyuubi was close to pull away all of Narutos chakra and use it to free itself from the seal. In the process, Narutos chakra and thus a bit of its hate would get transfered into Kyuubi.
So the point is, all the hatred was accumulated into the tailed beasts from people(specifialy theyre chakras emotional natures) who tried and failed to gain control over theyre chakras. Thats why I think Kyuubi has the most of the hate out of all tailed beasts, the stronger the chakra of beast is, the harder it gets to gain control over it. Since Kyuubi is the most powerfull, its most likely that he had the most succes in taking over his hosts chakras completely.
My guess is that most of the people who tried to use Kyuubis chakra were from uchiha clan since theyre occular powers were the best shot at subduing Kyuubi. And since uchiha clan is the way it is, the more and stronger hate was accumulated in Kyuubi.
This would also mean that there could be a way of purifying the tailed beasts, or unleast shift theyre wild behaviors a little. Just like Killer Bee managed to with Hachibi, I guess it was no luck but as a result of Killer Bees chakra. We will see what happens to Kyuubi, for now there is a little progress since the latest chapter.
So what do you think ? Possible or not ? Let me know if something doesnt make sense.
You may have your own take on this theory, maybe someone can find an evidence to support it, or to prove it wrong ?