Devin – thanks for your thoughtful reply. I appreciate your perspective. Sure, you will always get unqualified applicants, but consider this... Joe and Jane—two people with different skill sets—may both apply for a job called UI/UX Designer. If the role you're trying to fill will be focused primarily on creating beautiful user interfaces (Joe's speciality), you just wasted your and Jane's (an interaction designer) time. Jane may tell other designers, Devin doesn't understand design. This may hurt the reputation of your business and make it harder to find talented designers in the future.
Designers have specialized skills—just like developers. If you needed to hire a developer to build an iOS application, you'd be better off hiring someone who specializes in Swift, Objective-C, and using Xcode. Yes, there are "full stack" developers who can work across a variety of technologies and programming languages. But, just like the unicorn designer, finding and affording developers who are truly skilled at everything is no easy task.