One consequence of this kind of character presentation is that audience members can experience a sense of "she deserved it" when something bad happens. Take, for example, the domestic violence depicted in the Schuester kitchen, where Will grabs Terri, shoves her aggressively against a counter, and yanks at her clothing, all while she pleads with him to stop. This scene was not read as domestic violence by many viewers, because, well, she deserved it. If she hadn't been manipulative, he wouldn't have been "forced" to act in the way that he did.
This plays out continually in pop culture, where mentally ill characters are subjected to brutality and it is read as acceptable, appropriate, or even necessary in some cases, because of how their mental illnesses express. The symptoms and expressions of mental illness are not always easy to control, even for people receiving appropriate treatment, even for people who very much wish that these things didn't happen; it's not that people enjoy violent outbursts or crying jags or hallucinations. When viewers of pop culture receive the message that it is OK to behave abusively to someone because of mental illness, it sets a dangerous precedent.