The problem is not merely that Michelle Wolf's act was unfunny, gross, and demeaning, or that her voice is singularly annoying. The problem is that it will now be treated as rightful fodder for those who will claim that Trump's decision not to attend was entirely justified. Even if his supporters were on the fence on that question before, this surely will persuade them that Trump made the right choice. Selecting Wolf was a profoundly bad decision, and one that does nothing to advance the goals of the first amendment.
Here's a link for those who missed it. Don't watch with children around unless you are wearing headphones.