Earlier quoted context omitted.
You are happier to have your resources stolen and not be aware of it (it's invisible, you can't see what's happening and react - right?) than to be shown an annoying thing which is very much in your awareness? I don't know, I'd rather know someone is harming me silently and have the means to stop it by default. The things that are shown in front of me, I can handle them...
My computer is at maybe 20% resource utilization while I'm browsing the internet. Resource utilization only becomes a problem once you run out of resources; there is zero difference to me between 20% and 40% resource utilization other than very minor factors like a negligible increase in power draw and my fans spinning a little harder. Of course people could (and do) build malicious mining scripts that try to use way…
However, a large portion of devices on the internet run on batteries, and don't have huge quantities of reserve power.
Back to things such as desktop computers, though: am I supposed to close my browser before doing anything CPU intensive?
Someday, will I need to close StackOverflow to avoid negatively impacting the time it takes to compile my code? That's a trade-off I'm not willing to make.