In my particular situation, actively malicious filenames are very unlikely to occur (and if they do, it implies that I have much bigger problems than this program can possibly address or even meaningfully exacerbate).
However, I still don't want the thing to fail to work correctly if a filename happens for some reason to contain quotation marks.
Quotation marks are entirely plausible (and single quotes and spaces are absolutely guaranteed to occur), since some of the filenames in question will be created by people who don't know the difference between a document and a window, much less what a shell is or why including arbitrary punctuation characters in a filename might have unexpected consequences. They'd probably put newlines in filenames if standard file-save dialog boxes provided an easy, discoverable way to do so. (Just to clarify, the preceding observation is most definitely not intended as a feature suggestion for widget set makers. I was annoyed when standard GUI file save dialog boxes started making it easy to put spaces in filenames; but there's clearly no way to go back on that now.)