From a legal standpoint, running arbitrary javascript code is not breaking the law. Mining crypto with a website isn't a problem at all.

My own site does this. (Micro earnings crypto site).

The issue is when they hide it.

The earnings are abysmal. There is a reason it hasn't been more widely used. But as an accomplishment, it is pretty darn cool. And hopefully can find a niche to be worthwhile in.

Basically, I think it's all in how you use it. If I add tons of hidden ads to my site, I'm a thief stealing from advertising companies. But if I use them in their proper place, as they are meant to be used, I'm just a smart businessman.

My 2 cents, anyhow.