the scriptwriter was under investigation by HUAC at the time, and so for him it was important that the villains be *openly* defied, rather than outwitted.

If we're talking Doylistically, I suspect it was important to Fred Zinnemann as well. (I know he made all sorts of movies, but High Noon really played like a mirror-flip of Act of Violence for me: what people will stand up to, what they'll stand up for.) But I do think it works on the Watsonian level, which is probably more important.