What Is the Rationale for Laws That Provide for Legal

What is the rationale for laws that provide for legal verdicts of "guilty but mentally ill?"

A) to prevent the truly insane from being treated as criminals.
B) to provide treatment options for convicted criminals while still holding them responsible for their actions.
C) to deal with mentally ill vagrants.
D) to permit consideration of whether the accused could appreciate the wrongfulness of his or her actions.