Sonya sets up an either or scenario: either one has a mind clouded by illusion, or one will have their emotional outlook tainted. While it may be possible to have both of these things, we know, if her statements are true, that everyone must be tainted or clouded by illusion.
We can prove D to be true if we believe Sonya. Since everyone must be either tainted or clouded, if someone is not tainted, their mind must be clouded by illusion. Thus, everyone whose outlook is not tainted must have their mind clouded by illusion.
B takes what is true of each individual, and falsely generalizes it to a whole group. The idea that (as B states) either no one is tainted, or no one is clouded ignores the possibility that maybe half of a group is trained and the other half is clouded. While we know that each individual must be either tainted or clouded, it is possible that within a group of individuals, some are tainted, and the rest are clouded.