I would argue that it is unethical and becoming illegal to a certain extent in various jurisdictions (such as EU). It is taking a similar process to the use of

I would argue that it is unethical and becoming illegal to a certain extent in various jurisdictions (such as EU). It is taking a similar process to the use of unsolicited email mass-marketing we now consider SPAM. In the early days, it wasn't obvious how invasive SPAM would be, but in hindsight it is very clear and now there are laws to discourage the practice.