This discussion has in a large way gone both out of topic thematically and somewhat sour in the atmospherics. Let me take the time to reply to the various contributors in a lengthy but hopefully clear way.
I will firstly expose what constitutes a constructive edit as well as some foreword about what I understand as a healthy discussion. Secondly, the main arguments against forest micromapping as well as the result of my reflection on these arguments will be outlined. One of these arguments will most likely change the way I map forests and should probably be used as a good practice for the wiki. Thirdly, I will refocus on the main topic and expose the problem of the destructive edits. Finally, I will propose a metaphor of my own way to see the whole thing.
Constructive edits and constructive discussions on OSM
A constructive OSM edit is an edit that brings the data closer to the physical world on the base of sources compliant with the licence. Bringing more accuracy with "illegal" sources isn't a constructive edit just as mapping false features. In addition "spam" exists when either untrue or unnecessary data is added, such as an additional node in a straight way for instance. I will elaborate more on this particular point later as I feel that there is ground for improvement on my side on this particular topic.
Regarding the atmospherics, this discussion has triggered expressions such as "give up" or "frustrating", which I deplore. I assume that all the participants of the mailing list and most OSM contributors act and speak in good faith. That being said, prescriptive orders or semi "threats" from individuals taking upon themselves to speak in the name of the community sound very much like a mexican standoff. I am afraid to say that those who confuse a genuine OSM contributor with a Western criminal are in the wrong film. I like Sergio Leone movies but we are amongst volunteer contributors using their free time for the sake of an open source project. I have never destroyed good data, duplicated data nor used non compliant sources. The tone of the discussion seems therefore at times inappropriate considering the context. To which I confess I tend to escalate further, which isn't smart.
Let's review some of the arguments against forest micromapping. I will regroup them but I hope to cover all of them.
The "data overload" argument
This is an argument to protect the server's load but I believe that no one should map for the server. However, there is a gray zone, on which I will elaborate on the "node density exceeding the imagery" paragraph.
The psychological / motivational arguments
No one knows why other people do stuff. Why do some users map dog waste baskets and others brothels, police stations or individual trees? No one knows. I suspect that a large part of the reason is unknown to the users themselves. However, making hypotheses on someone's motivation on a public mailing list isn't only irrelevant, it inevitably leads the discussion towards straw men and toxic atmospherics. The topic is certainly interesting for an academic paper in psychology but irrelevant to this discussion and most of the time toxic.
The "wrong mapping according to the newer imagery" argument
It'is the life of most OSM data : it gets improved with new sources. Most buildings can be redrawn with newer imagery. 3D people might redraw them using photogrammetry. The continental shift is, in a very small way, putting a time limit on all the data. All these things are true and at no time am I trying to suggest that all the detailed forest should be considered as sacred or definitive. I hope that it is clear: as with the rest of OSM, forests should be corrected and improved with newer sources. It isn't specific to the forest, though.
The "node density exceeding the imagery resolution" argument
It probably comes from Sarah and it did trigger some thinking on my side. I suspect that, as I did some of these edits mechanically while thinking about something else, I didn't always consider the level of zoom in JOSM. It is likely that we find ourselves close to the "involuntary spam" gray zone as the same level of accuracy regarding the imagery might be achievable with less nodes in some cases. I will certainly pay attention to that in the future.
The "changing nature of the forest" argument
Very true, the vegetation changes. The same applies to all data. Buildings are constructed and demolished. Businesses open and close but are mapped anyway. While I don't like to speak about motivation, I suspect that it might be interesting to study the evolution of vegetation over time with vector data in the future.
The "unclear limit of the forest" argument
It is a fact that there is no clear way to decide what constitutes the exact limit of a forest. But again, the same applies to all the buildings (I suspect that many are mapped according to the roof and not the walls) and almost all OSM data.
Rivers are often mapped with both an (imprecise ) area as well as an (imprecise) way. Towns get mapped with both a node for the center of the town as well as an area for the residential area of the administrative boundary. The same logic could be applied to trees (area for the leaf cover and node for the trunc, which would be more precise that the center of a village or a large river), although I have no intention of doing so. This topic, as almost all features, is the consequence of the mapper assessment, the mapper time dedication, hopefully some general good practices as well as the sources used.
I hope that it summarized in an honest and comprehensive way the arguments of the discussion. It does as I have understood them at least.
The destructive edit problem
Now to go back to the initial topic. It certainly wouldn't be a problem to simplify what I have called "involuntary spam" provided something like that is actually there. Removing nodes exceeding the image resolution is desirable and I am not talking about that when I discuss this particular case of (probably well intentioned) vandalism. Using automated tools to "simplify" creates forest where there are no forests, sharp angles where the forest is smooth. This is what I call a destructive edit (it regresses the data away from the physical world) and constitutes the initial concern triggering the discussion. It is one thing to map according to one's own vision of what OSM should and shouldn't be. It is a complete other thing to actively degrade the existing data according to this subjective vision. I still don't know how to address that problem as the discussion stayed most of the time out of topic.
The metaphor
The reason why this discussion has also been frustrating from my point of view is the following.
It's like a person voluntarily cleaning a street and removing litter to improve the neighborhood. This person might be a weirdo as she uses a toothbrush instead of a broom to clean particular places in the street. Now comes another person dumping garbage on the street. The original volunteer addresses the problem to the municipal council and the discussion focuses only on how bad it is to use a toothbrush instead of a broom. Some members of the council also argue that it is customary to clean the street from east to west and not the other way around while another municipal councillor issues threats against the volunteer cleaner.
As all metaphors, It is debatable but it does at the very least outlines my own subjective perception of the discussion.
Let me reiterate my hopes that everybody feels understood as well as the hopes that some will sincerely consider my arguments as I considered theirs.
Regards.