The fact that Bitcoin transactions are broadcast to the entire network should tell you that you are way off. Think of all the work that goes into processing a VISA transaction, and then imagine if tens of thousands of other payment processors had to do the same work.
"Processing a transaction in the VISA network" != "securing the monetary system".
First you have to have the VISA network in the first place, that's no mean feat. Then there are the banks themselves, hardly trivial. Only then do we get into central banks and financial regulators. All part of the package.
The same sort of reasoning applies to Bitcoin. Someone has to secure all that Bitcoin mining hardware, and as the effort that goes into mining grows, the energy spent on securing mining hardware will grow. I would also include the cost of producing ever-faster mining hardware; honest miners have to continuously upgrade their equipment just to keep pace with attackers.
Really though, the fact that every single transaction is broadcast and that every single transaction must be verified by the entire network (in theory) is what kills Bitcoin's energy efficiency. Whenever a new mining rig is brought online, the energy efficiency of Bitcoin decreases -- and Bitcoin is designed to incentivize bringing more mining equipment online.
> Really though, the fact that every single transaction is broadcast and that every single transaction must be verified by the entire network (in theory) is what kills Bitcoin's energy efficiency.
It is also the fact that ensures it's distributed nature, and the purpose of its very existence in the first place (we have plenty of centralized digital currencies).
> Whenever a new mining rig is brought online, the energy efficiency of Bitcoin decreases -- and Bitcoin is designed to incentivize bringing more mining equipment online.
This is not necessarily true. The efficiency (number of SHA256 operations per joule expanded) will increase over time. It has already increased by a factor of 1000 compared to CPU mining. So it's definitely possible for both the security and the energy efficiency to increase simultaneously.
