Hahahah...

Maybe the EMS has the abiltiy to controll other Sharingans, lol.
Itachi, who knew this, bravely fought the evil thing in his mind, to test Sasuke so he can avenge he and his family. Thus with the on and on that HES evil making Sasuke putting more effort in it.

If Madara could controll the Kuyuubi, why not randomly controll anything else?