I wasn't familiar with the author before this article. You can see his wikipedia page here:

https://en.wikipedia.org/wiki/Bradley_M._K%C3%BChn

He is best known for his efforts in GPL enforcement,[7] as the creator of FSF's license list, and as original author of the Affero General Public License. He has long been a proponent for non-profit structures for FLOSS development, and leads efforts in this direction through the Software Freedom Conservancy. He is a recipient of the 2012 O'Reilly Open Source Award.

Excerpt from the first part of the piece:

In this philosophical essay, I explore the question: “When (if at all) is it ethically and morally acceptable to use proprietary software in the production and/or improvement of urgently needed copylefted FOSS?”

The question presents a complex conundrum. I attempt herein to rigoriously examine it through both a priori ethical analysis and a posteriori (and folksy) consideration of my personal experience and the shared experiences of the early software freedom movement.

I surprised myself at the outcome of my analysis. I conclude that under some circumstances (of which we have already witnessed in key historical examples), use of proprietary software by FOSS contributors to create/improve FOSS becomes a moral imperative. And, that imperitive often supersedes the moral imperative to avoid using that proprietary software.