Sanji doesn't hate himself. The absence of love is not hate. It's indifference.
What Iva noticed about Sanji is that he fights like someone who doesn't care about getting hurt. It's not suicidal, but it is unhealthy and dangerous, like Gaban said.
This tracks with the fact Sanji only became strong for others. First Zeff, then Luffy and his crew.
In essence, Sanji is a lot like Ace, another "imperfect Conqueror" in the story. The value they attach to their lives is determined by what they do with it on behalf of others.
That will not suffice for Conqueror's Haki. Sanji can only become a King for himself.