Dangerous people should not have access to fire arms. On this subject there seems to be near universal agreement. Laws, regulations, and enforcement are required to intervene and prevent people who are dangerous from purchasing or possessing fire arms.
Controversy arises largely in the defining of dangerousness. Mental health professionals fear the mentally ill generally will be further stigmatized and isolated. Civil rights defenders fear abuse of civil rights without clear definitions and strict adherence to due process. These are legitimate concerns that must be addressed in the development of policies.
There are existing federal and state laws that prohibit specific categories of dangerous people from purchasing fire arms. For example, people involuntarily committed to a mental institution, or found not guilty by reason of insanity, or who committed a violent act towards others and are the subject of a domestic violence restraining order, or have been convicted of a felony, or have been convicted of a domestic violence misdemeanor.