For "Engineer" I entirely agree, that is a person who has received the required training to be accredited as an Engineer. I am not an engineer, and I vigorously defend the right of engineers to be identified as such, and everyone else not. Hobbiests, train operators, office equipment repair people, and people who work in kitchens are not engineers (in that role anyway), and should be denied being referred to as such by society. 'Same for "Doctor", you are, or you are not, an accredited certificate says if you are.