> It's called an externality. It doesn't matter if you'd pay $10 for it if the cost imposed is too great

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