Hashrate is also limited by design:

https://en.bitcoin.it/wiki/Difficulty#What_network_hash_rate...

Each miner has an incentive to outcompete other miners. A mining cartel can agree to keep difficulty and hashrate low. It is also comparable to a truce in a military conflict.

> "A mining cartel can agree to keep difficulty and hashrate low."

Won't work. If a mining cartel agrees to keep difficulty and hashrate low, they're just making it easier for those outside the cartel to mine more Bitcoin.

With unused mining hardware reserves they could smash outsiders by ramping up the hashrate.

Cartels usually don't last forever, but they can last for a while. In the case of bitcoin, it could reduce total energy consumption.

In one comment you're suggesting a cartel should keep the hashing rate low, in another comment you're suggesting the same cartel should increase the hashing rate to keep out the competition. What are you really proposing? Keeping it low until any form of competition shows up? That competition is always likely to be a factor for as long as Bitcoin mining is popular.

> Keeping it low until any form of competition shows up?

Exactly. This is similar to how price dumping works: https://en.wikipedia.org/wiki/Dumping_(pricing_policy)

You're not listening. I'm suggesting it'll never work for Bitcoin as the available competition is ever present. A cartel gains nothing by mining at a slower rate.