So I've used <I>plenty</I> of STL functions which takes functors as parameters. For calculating set differences, for sorting vectors, etc. I'm in a situation where I'd like to write such a function ...

Anything, and I mean ANYTHING, can be abused in coding. Your prefered style, paradigm, or TLA of the minute is not an exception. If you can dream it I can abuse it. If you judge a feature of a ...