Okay, so having a mental disorder means they should have their children taken away? There are A LOT of people with bipolar and/or schizophrenic disorders that don't murder their children. Homicidal tendencies is not even a symptom. People who are depressed (also classified as a mental disorder) are more prone to homicidal tendencies than the schizophrenic or bipolar.
You just can't try to take away people's children based on their mental health, with no history of abuse or neglect. What about a mental disorder that is well-controlled, or no longer present? Would you want to seek treatment knowing you risk having your children taken away?