One early practical reason was how many people you can realistically put in jail in one go. Doesn't hold water for this long, mind.
How you deal with "smaller cogs" is something we should get better at though as it doesn't just apply to Nazi Germany. Actually, read on not thinking about nazis but the hundreds of authoritarian regimes that have been in place across the world since. This is current stuff, not ancient history.
I disagree with the B&W statement "was part of the machine". In any situation were civil liberties are suspended/compromised you will have sadistic monsters rising to the top. Shit floats. Now, many regular people find themselves in the machine, surrounded by people they despise that are doing some horrible things. What do you do?
Most here are posting about how you willingly take part, nobody makes you do it, etc. Firstly, not everyone is cut out to be a freedom fighter both in temperament or whether they can be much use for any amount of time. Many will say they want out, risking getting a big target on their backs, but largely will go on to live a "normal" life with their conscience clear. Then there's those that fight from within. The more ballsy ones get to positions of influence and use that as cover to actually do good stuff unnoticed. For the most part though, you have people whose reasoning is that it's better for them to fulfill their role than some nasty fecker. They play along with a lot, they just have to, but occasionally can get a small win here and there.
I'm not saying that is the case here, very much the opposite. In the aftermath, these "small cogs" become really valuable sources of incriminating intel. From what I read this woman was twice in court as a witness 60-70 years ago and adhered to "didn't know what was going on". Should have wound up in jail there and then if you ask me, and that in turn would have made tonnes of cogs fess up and bring light to key information in a timely fashion.
It's a pretty key issue. You don't want impunity or passive acceptance of bullshit excuses. On the other hand, with "anyone that is part of is guilty" what you get going forward is even more monolithic machines with no sprinkled "good ones" driven by the occasional opportunity to make a small difference, which can be huge for AN Other, and certainly add up to a lot.