I'm aware of those studies, but skeptical of some of their methods and claims. I'm especially skeptical that when they claim causation and not correlation.

In any case, there's a big difference between 'spammer' and 'bad-boy' as well as a big difference between demonstrating the success of a strategy and demonstrating it's prevalence.

Edit: There may be some good studies demonstrating causation but I am not familiar with them.