wheel - 5:15 pm on Dec 21, 2010 (gmt 0)
In fact, your proposal was the previous approach that we were using. At the same time, we would leave a message in the webmaster console and often try to email the site using email addresses that we could find on the site. What we found was that we weren't reaching the site owner as often as we wanted to. Many sites remained hacked for days, weeks, even months despite our best efforts to alert the sites through other methods.
You're not the internet police. It's not your responsibility to clean up the internet.
If the concern is the USER, then remove the site from the serps immediately. that fixes the problem doesn't it? And that's Google determing on their own what they want to serve to visitors.
Deciding you have some need to alert webmasters to problems, for sites that are no longer in the serps has nothing to do with the user. In addition, you are providing clearly negative commentary about someone's site. That's got nothing to do with a positive user experience, not when the alternative is to just remove the page/site.
In short, if the problem is in fact to look after the user, remove the site. If the problem is to notify the webmaster, well, why is Google making that their problem again?
Which is why some may be led to believe that Google's not doing what it's doing for the best interests of their visitors.