The main issue here is that Kanye's antisemitic speech doesn't come from within himself or his own mind
it comes from outside influence...
The hip-hop/rap world is completely indoctrinated with the ideology of the Black Hebrew Israelites, an extremist ideology that teaches afro-americans a dangerous form of antisemitic views.
The part where Kanye's says "the funny thing is I can't be antisemitic because black people are actually Jews" comes from this ideology.
An ideology that is mainly spread by Louis Farrakhan, the leader of the black supremacist organization NOI.

Here is Kanye alongside Louis Farrakhan and hip hop artist Vic Menza:
http://ibb.co/D9YHJS7
Here is Kanye's whole family alongside Louis Farrakhan (in white):
https://ibb.co/sF5S4VB

I agree that Kanye's mental health isn't in good shape, but antisemites like Louis Farrakhan take advantage of Kanye's situation in order to push their indoctrination even further.
Louis Farrakhan knows the level of influence that Kanye has in the black community.

Americans against Antisemitism video on Louis Farrakhan:
https://youtu.be/EJWisPxEGxY