Personally, I find it valuable to question generally-held assumptions. Many of the greatest advances in human progress began by having the courage to question unexamined assumptions that most people took for granted at the time.
If the assumptions are warranted, then there is no need to fear. They will stand up to scrutiny.
However, if they turn out to be unfounded, then we will have discovered something important and taken one step closer to the truth. Sunlight is the best disinfectant.
In the case of a deadly poison, where even a tiny bit can be harmful to the body, that sort of classification makes sense. However, when it comes to classifying the terms under which software is distributed, that principle doesn’t seem to apply. Installing one piece of non-free software on an otherwise free system doesn’t harm the system as a whole so long as that piece of software itself is not harmful, and the action can easily be undone. This is quite different from a human ingesting something laced with a deadly poison, so I find these two scenarios to be rather disanalogous.
Some zealots seem to view all free software as good and all non-free software as evil. Perhaps that’s the motivation for requiring strict purity (the 100% requirement). However, these advocates should recognize that by allowing such value judgments to infect their classification scheme, they risk its credibility. The classification scheme itself should be neutral and objective. Let people make their own value judgments later. From this perspective, the stricture that even a single line of non-free code in an otherwise completely-free software compilation renders the entire thing non-free looks, from the outside, like nothing more than arbitrary puritanism.
To return to our earlier analogy, the reason the USDA Organic seal requires only 95% organic ingredients is, presumably, based on the recognition that 100% is impractical in the real world, where the realities of farming and manufacturing means that it is inevitable that a small amount of non-organic food will make it into many final products. It’s presumably also based on the recognition that there is considerable controversy over whether organic food is superior to conventional food. It would be improper for the classification requirements themselves to take a stand on that debate. Their job is simply to tell us which is which, not which is better. By the same token, the FSF would do well to recognize the practical requirements of running code on real-world hardware and accept the reality that a small amount of non-free code will make it into many otherwise-free products (at least those that can be relied upon for any use case where security matters). As things stand, their insistence on using their classification scheme to try tell the world which is better appears to have rendered it largely irrelevant to the rest of the world as a practical tool to which is which.
I see little reason that Debian, Fedora, Qubes, or any other operating system with a significant userbase should pay heed to a standard that is not fit for purpose in the practical world of computing on actual hardware and real security needs. Therefore, I reject the assumption that a compilation of software must be composed of 100% free components in order for the compilation as a whole to qualify as free.