> The Carnegie approach thus described makes it very easy for devs to notice the encouragement and ignore the suggestions of criticism.
This is definitely true, I've seen it too. Definitely something to watch out for.
I guess at the end of the day I think it comes down to "know your audience." Similar to the Principle of Least Privilege I like to follow (what I call) the Principle of Least Criticism. Don't use any more criticism than what is necessary, but (and I suspect this is where we will both agree) you need to use enough criticism that the person understands your point.
With that said there might be some significant limitations on the approach. The principle one is that it relies on knowing the individuals involved fairly well. This is easy in a close-knit and small startup environment! It could perhaps be more difficult in a sizable enterprise or open source context where you don't know the other party, don't have time to build a relationship, and/or can't rely on a long conversation to slowly build up to the least amount of criticism required. There's also the question of how to handle groups or meetings in which different people have different thresholds. When one person's minimum required might be someone else's excessive negativity and they're both in the room, there might not be a winning outcome with this approach.
Knowing your audience is an excellent and wise maxim to live by. It might not always be as simple to live by as could be hoped.
Thanks for the discussion