The cynic in me sometimes wonders if this argument is used as a red herring, and that there are other issues that need sorting out (involving money and control).

Of course there are control issues as well, turkey has 73 million population and so would instantly be the 2nd largest voting bloc, very likely to become the biggest due to demographics in the future. It would make sense to have a much stricter standard for accepting large than tiny countries as new members.