We just have to wit for kishi but why else would the sharingan look like the juubi's eye and why such evil things to obtain power? sounds like evil juubi to me.
Well if u consider it this way:
1. MS needs grief of losing closest to u. Is it evil? No, loss teaches us to value life and to love.
But the few greedy people take the short cut and kill their closest people to get their MS earlier.
2. EMS needs ur sibling to be ur equal in every way (Have MS at least, and thus equal) who must trust him with his eyes. (U cant just take it forcibly from ur sibling when ur blind can u?). This is the mark of trust and sacrifice.
So actual requirement of Sharingan is love, trust and sacrefice. Much like the buddhist principles of overcoming Samsara through Nirvana which in turn is reffered to as Rinne the endless cycles life and rebirth . . . . . Which in turn would mean that mastering Sharingan leads to overcoming life's boundaries and attaining Rinne.
Kishi is heavily dependent on Shinto and Buddhist myth for naruto, Belive it! Or Research it!
Also see what tomeo really is:
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