Oh come on.
Kakashi got it from the death of Obito.
That theory is flawed.
1. If Obito is in fact Tobi (which I hope is untrue) he isn't even dead.
2. Although Kakashi was in a team with Obito they were not best friends. They were rivals all the time. Not to mention the Kakashi we know from the beginning of the Kakashi gaiden didn't seem to care about something like friends.
I doubt he had a best friend.
In the gaiden they became friends. But only for half a day maybe, before Obito got killed.
We saw the whole story. You tell me they were best friends?
Also Kakashi didn't kill Obito. Not even close.
I doubt feeling guilty or responsible for the death of a friend and actually killing him yourself is the same thing. Not even close.
Because if you live the life of a shinobi friends die all the time.
If the incident Kakashi had, led to him gaining MS, many other Uchiha would have been able to do the same, since it's not that uncommon.
Lastly we don't even know if what Itachi said is true. He could've been lying and faking the scroll.
And we know Shisui was supposed to keep an eye on Itachi. Maybe he killed him because he was on to him, instead doing it to gain MS
"For Feanor was made the mightiest in all parts of body and mind, in valour, in endurance, in beauty, in understanding, in skill, in strength and subtlety alike, of all the Children of Illuvatar, and a bright flame was in him"