Thanks for looking up some examples!

> :secure
> :use-gui
> :save-<something
> :allow-includes,
> :double-click-to-zoom
> :require-force-option

> These all make sense as #t
> in their contexts, and negating them would IMO make them harder to
> understand.

Without seeing context, I don't see how it would hurt these cases. The
point of giving an optional (keyword or positional) argument is to make
the procedure do something exceptional. If the interface is designed
well, the exceptional thing is more surprising than the default thing.

E.g. (http/post "https://foo.org/bar" ... :insecure? #t) really calls
attention to the fact that it's insecure.