> Plus, we have a lot of processing power on the client side, which should be utilised.
It would be one thing if this was a matter of consent. It isn't. It uses your resources without your permission. Leaving JS on is not permission to consume as much CPU as you want (otherwise, every website would also run a crypto miner).
> If a site uses it badly, just don't go to that site.
This sort of blitheness is very surprising to me. What if we're talking about a passport site, or an unemployment benefits site, and so on? Why is the onus on the user and not the developer?