Thats can be argued for and against. Both sides have decent arguments to support their views. Immediate reaction to the words "mental illness" is "dangerous", but thats not what reality and data suggests.

Someone who has depression still has a right to defend themselves, especially if they are older and physically weaker and unable to protect themselves through physical means.

Some of these people, due to financial strains, live in high crime areas and are vulnerable... You can word it in such a way as to make it seem like allowing them to exercise their rights as a citizen is bad and dangerous, but that would just be a lie.