How can beaver dams be considered good for the environment but man-made dams get so much resistance despite producing some of the cleanest energy and reducing carbon emissions?
Surely humans know how to design/divert waterways better than a beaver.
"The environment" is a really big subject. It's like saying "How can chemotherapy be considered bad when it actually helps cure cancer?" You can see how in this statement things are confusing because chemotherapy is very dangerous and harmful, but in a bigger picture, it's very helpful and life-saving.
A man-made dam is good for the global environment when it offsets coal burning. A man-made dam is terrible for the local ecosystem when it completely obliterates the local ecosystem by putting it underwater. It also has much more surface area for evaporation than rivers leading to water loss. They also promote extreme anerobic bacteria compared to rivers causing dramatic increase in greenhouse gas production in the water. Dams also prevent rivers from delivering silt, nutrients, and other things that help Ocean ecosystems including reducing the oceans ability to sink carbon. They also can contribute to earthquakes. Finally, once they fall into disrepair, they become a huge dangerous hazard and most countries do not want to pay to maintain and decommission.
So is a dam good or bad? It becomes a question of the net benefit. For the chemotherapy, we say that there is a net positive benefit. For man-made dams, there is a current debate and I won't say what I think.
And finally Beaver dams are often considered good because they are not large-scale. They don't flood a whole region, they just slowly turn a small area into a wetland. They slow down fast-moving streams, reduce erosion, provide buffers against storm surges and help control flooding. Beavers can be a keystone species and a healthy beaver population has a dramatically positive effect on the local ecosystem.
Surely humans know how to design/divert waterways better than a beaver.