With vices I suspect that it isn't just the activity concerned but the purpose, which varies from person to person.
e.g. TV can be used to educate but it can also be used to distract
That said, some vices may be worse than others. In the case of social networking, I guess the obvious alternative is going to parties which are OFC a gateway to alcohol consumption.
If a vice is less harmful but more widespread is it better or worse than the alternative? E.g. Facebook vs. World of Warcraft