Monero Javascript miners are common to this day.
They're an easy way to donate to people in places where it is hard to transfer money. What exactly is the argument you are making here? Presumably the people running those things are definitely paying for their power one way or the other.
They get delivered through ads and sites directly in order to steal further resources from unsuspecting site visitors.
The days when this was either widespread or not blocked by mainstream browsers are behind us. At this point it is mostly scaremongering for no good reason.
Define “common” and provide sources for your claims please.