For safety, the regulation of fraud and crime, not to mention bullying and harassment - I think everyone should be issued with one email address only. It should be impossible to have multiple online personas - you should be forced to be yourself everywhere.
I read so much about the evils of the internet (OK, have just spent a few days with Torygraph reading in-laws), but I do think there is an horrific, murky world on here that is having harmful effects 'irl'.
Arguments against - "but the internet helps so many people talk about problems and get support". Possibly it does. My own experience is that some of the most hurtful and serious problems are disbelieved by about 50% of respondents, rising to 80% by about the third page or so. And a lot of the advice can be completely misguided and frankly wrong when it comes. Plus, there already exist many organisations that people in real need can contact with trained volunteers/staff there to help or just listen.
I think this might be the way the net is headed - I hope so because our police force simply can't keep up with the workload and the crime is very real, and I think, outweighs the benefit of having a bit of a laugh without anyone knowing its you (frankly, who cares its you anyway?).