Same thing when humans build dams, right? We're creating new ecosystems.

Is that a rhetorical question? There's quite some difference between a 200m tall concrete dam that holds 1m+ cubic decameters of water[0][1], and a bunch of twigs and logs jumbled in a creek that might be 2 meters high on average and actually house life like beavers, frogs, birds etc.[2]

[0] https://en.wikipedia.org/wiki/New_Bullards_Bar_Dam

[1] https://en.wikipedia.org/wiki/Environmental_impact_of_reserv...

[2] https://en.wikipedia.org/wiki/Beaver_dam#Benefits

So whether something is natural is a matter of scale?

If we cut down 1,000 acres of trees for wood, is that natural?

What about if a beetle infestation destroys a million acres? Still natural?

1) Was the beetle introduced to the area by humans (which is the case for a number of pests)

2) Were the trees killed made susceptible to the beetle because of heat stress, possibly caused by human driven climate change? (this is the case for some large scale infestations)

Overall, the point is; yes, where imbalances in nature are triggered by natural causes, there is no issue with that (earthquake, hurricane, long term climate oscillation).

Where imbalances in nature are triggered by humans, (IMHO) we should quite naturally regard that as a negative since a) we are intelligent enough to find ways of avoiding environmental degradation and b) Environmental degradation has both consequences to other forms of life as well as other humans.

I guess you're playing devils advocate here, but you're hardly adding to the conversation.

I’m challenging the predominant belief that anything humans do is “bad and unnatural” and anything animals do is “good and natural”, even though man is just as natural as any other organism on earth.

That premise doesn’t really hold up to rationale examination.

To continue the thought experiment, if the beetle infection was not due to any impact of humans, should we try and stop it to preserve the forests? By the above logic we shouldn’t because the destruction is “good and natural” and we would be interfering with nature.

The universe is indifferent. Humans don't have to be.

Human indifference isn't a binary state. I can drive around in a big SUV, doesn't mean I'm indifferent. All the people in the world can't, nor are obligated to care exactly as much as you do. Telling people otherwise is just moralising.

Humans are a subset of the universe.

Actually yeah, it's all a matter of scale. Of course we are animals and what we do is perfectly natural, like a volcano blowing up, any other species that had been so successful evolutionary speaking as ourselves would be doing the same thing. But that does not mean it is good for us or that can keep going on forever. It is probably what made us successful that will destroy us.

Get back to me when beavers are causing the extinction of thousands of other species and arguing about how to warn their descendants about radioactive waste.

Many species have caused widespread extinction on a level humans have barely approached. Cyanobacteria, for example: https://en.m.wikipedia.org/wiki/Great_Oxidation_Event.

The problem is that beavers didn't suddenly start doing that, the ecosystems they live in co-evolved around the existence of beavers.

On time scales relevant to evolution, human civilization is happening in an instant and nothing can adapt as fast.

The result is a gigantic loss of biodiversity.

Bacteria can mutate quite quickly and wipe out an entire species pretty fast, reducing biodiversity.

Can they wipe out thousands of species?

Yes: https://en.m.wikipedia.org/wiki/Great_Oxidation_Event

Wait, that says it took around 0.3 billion years, and when there was only single cell life, we have no clue about the biodiversity at that point in time. It cannot compare in time scale, and we have no clue if it can compare on biodiversity scale.

The point that's missing from this discussion is that beavers have been building dams for an eternity because it's part of their natural behaviour. The ecosystem has had ample time to adapt to it. An ecosystem is a delicate balance between systems that results from these systems co-evolving in the same environment for millions of years. The systems (plants animals seasonal change, climate) are all highly fine tuned to each other. Yes, this balance is sometimes abruptly disturbed under "natural" circumstances, but this is rare. What humans are doing in the last couple hundreds of years involves much more sudden changes to which eco systems have no time to adapt. It's the suddenness of the changes what's unnatural about it. Whether you call it natural or not is besides the point though. The point is that human dam building is a phenomenon very different from beaver dam building because, besides scale and impact, it did not gradually co-evolve with an eco system, but is an abrupt and disruptive change.

Actually beaver dams can be terrible for the ecosystem if you measure them the same way as human dams. They certainly can cause lots of death and flooding.