The cost imposed is proportional to the fee, since the fee has to pay for the electricity used to mine the transaction. And $10 of electricity is just... not a lot to worry about.
If you believe the electricity consumption in general has huge externalities, you have bigger problems than mining, and once you address those the mining cost/diffiuclty will adjust
No. Miners get rewards for mining blocks, which pay for 80%. Transaction fees don't pay for the electricity used in a transaction: not even close.
> If you believe the electricity consumption in general has huge externalities
Well, sure, I believe that electricity is artificially cheap. I also believe that spending $50+ of electricity per transaction done is absolutely nuts. And that amount is steadily increasing...
It's called an externality. It doesn't matter if you'd pay $10 for it if the cost imposed is too great. There are a lot of things people would absolutely pay for that we don't allow, because of that. Dumb weird fantasies about decentralization or counterparty risk or whatever don't actually matter if the energy cost is that high. It's just not important enough. Sorry.