I think this is a valid example of reasons where it would be helpful to know assembly as a C programmer, but not justification for the claim that writing C without knowing assembly is writing code you can't debug.

Even if you are having problems interfacing with a third party library, most of this stuff is pretty Googleable.

I think a good summary of my opinion would be that if you're going to primarily write C professionally throughout your career, it's best to understand fundamentals of assembly, but doing projects here and there? I don't think it's worth the time; you just won't use it that much.