That's like saying no one can be an artist because they're not a member of the official artist club. I'm sure the term engineer outdates any professional association.
Actually it's just being respectful. I'm not an engineer, but I work with a lot of engineers who actually have the qualifications to call themselves engineers, so if I call myself one, I'm essentially lying.
I am an Engineer, in that my degree is in engineering, and my job is in engineering.
I am not a Professional Engineer, in that I have not taken the Fundamentals of Engineering exam, passed, worked for at least 4 years under a Professional Engineer, and then taken the Principles and Practice of Engineering exam. So I can't put EIT or PE after my name, stamp projects which require it, or operate as a PE in any state.
I misspoke then. I would call you an engineer without your being a member of a professional association. I guess in my mind the degree is enough. I'll never have PEng on my business card, but you at least have the potential.