Think about it from the opposite direction: trust is a ridiculously effective optimization of group dynamics, and humans come equipped with it by default. It allows us to engage in trade and cooperation without paying the cost of perfectly, mathematically, enforcing the rules. It takes a problem that would be O(n!) and reduces it to something on the order of O(nlogn), at very little loss in the optimality of the result. Taking this shortcut is a no-brainer, it would be immensely stupid not to do it.
It so happen that historically, we took that trade-off and built a civilization on it. It worked well. It works well*. And what bitcoin does is trying to make our economy run on O(n!) overhead, because some individuals think that a political ideology based on not trusting other people is somehow a good idea.
That's a political opinion. But regardless of its validity, I'm not convinced that this justifies a single Bitcoin transaction producing as much CO2 as 700,000 Visa transactions.
A Bitcoin transaction on the blockchain is layer 1. A visa transaction is layer 3 or 4?
Lightning network is layer 2 and you could have >700,000 transactions in a lightning channel before settling on chain, so there you go Bitcoin layer 2 is more energy efficient than the common financial system layer 4.
You say pointless computation. I say layers on layers of security protecting the most sound monetary policy in human history