True, and I can just say that I'm a citizen of Canada, but unless I am actually that, I won't get any of the benefits or have any of the duties of a citizen of Canada. Similarly, anyone can just claim to be a Jew, but if they want to participate in Jewish religious (or even secular) life, they will sooner or later need to actually be Jews--they might get away with a charade for several years, but eventually it'll get out. They can claim to be a Jew all they want, but unless they actually are a Jew, it won't do them any good for any of the things they might want. I can go around calling myself the President of America if I really want to, but if I'm objectively not the President of America, or a Canadian citizen, or a Jew, and I'm saying that I am, I'm just delusional at best and a liar at worst.