Is stealing always wrong?:
If the person is mentally handicapped and can prove it-(Doctor supported diagnosis) then I don't suppose the person should be prosecuted.  BUT, if someone is supposed to be taking care of or has guardianship of the mentally handicapped person, they may be held liable for not fully supervising.    I also think HUNGER is a mitigating circumstance in any food theft issue.  If it isn't, it should be.