I come from an abusive family. In the past, moving on from that would mean simply moving to another town. With the internet, abusers are now free to stalk and harass regardless of geography; the old norm of pulling up stakes and heading on is gone. Requiring real names would mean that every jilted ex-lover, every insane sibling, every schoolyard bully can see exactly what you're doing, any time they want. Frankly, I'd rather deal with a few more trolls than deal with that.