"theory"
hmmm but kakashi took obito's eye, so he should have gained mangekyou automatically(Killed his best friend) well he did'nt really kill him but ya know? I believe instead because kakashi is not a clansmen, and had a moderate sharingan (2 Tomoe), this was flawed, so he most likely earned it thru training, He probly chooses when to use it because if using the normal sharingan, put that much stress on his body imagine the mangekyou? Anyways I don't believe in the "Itachi power transfer" was used on kakashi, sure Itachi can do it, but Kakashi's mangekyou (Black hole barrier) is completely different from Itachis' (tsukyoumi, amartseru, sennsu'o), wat really happened was Itachi did'nt want to kill anybody, although it probly would have made him a more convincing "S" ranked criminal, using Tsukyoumi on Kakashi was probly the most affective way to, neutralize kakashi without actually killlin him.