First, let me state that I am not arguing that people should not be professional or that what you are doing is wrong. Just offering a perspective.
I am curious as to how serious you are in saying this and what your hard-line is for correct spelling/grammar?
One of the first things I admit in an interview, is that I DO NOT have attention to detail. I am a big picture person and small details never really concerned me (with some exceptions of course). I have had a wonderful career with State Marching advancements, numerous sweepstakes, and several all-staters.
I have looked back at old resumes and realized they had a few sloppy errors but I am offered a majority of jobs I interview for and never had a problem getting interviews. I wonder if you might be overlooking some great candidates?
On the flip side with the technology available it is really easy to proof things these days or send your resume to several proof readers so there is definitely a limit as to the errors that are tolerable.