>I actually wrote a sed utility to collapse arbitrary whitespace

Can be done with tr, without writing a utility (if by "collapse" you mean what I think you do):

This file t:

$ cat t

the quick brown fox jumped

            over


            the lazy dog

containing many combinations of spaces, tabs and newlines (whitespace) can be changed to this file t2:

$ cat t2

the

quick

brown

fox

jumped

over

the

lazy

dog

by this tr command:

tr -cs "[a-zA-Z]" "\012" < t > t2

That also makes the output more amenable to further processing, including common tasks like finding the frequencies of the words in the input, as mentioned in the "More shell, less egg" post mentioned in this post:

The Bentley-Knuth problem and solutions:

https://jugad2.blogspot.com/2012/07/the-bentley-knuth-proble...