Requiring real names online would be the same as requiring we wear name tags--"Hello, My Name is Firstname Lastname"--in public.
Want to go to a coffee shop with some friends and talk about the latest Star Wars? Better bring your name tag so everything you say is correctly ascribed to you by all present.
Want to go wander around the farmer's market, talking to vendors about their products? Sorry, full name tag required so if you say something mean about someone's product, everyone will know who said it.
If tech companies are liable in the kidnapped kid+encrypted iPhone, wouldn't the same logic hold firearms manufacturers liable for crimes caused by the use of their product?
And now removing the fork from the light socket, a serious question.
The NSA employes many, many mathematicians and cryptographers. The NSA and GCHQ had public-key cryptography years before their re-discovery by public research. So if the government is so interested in finding a unicorn, why don't they foot the bill for searching for the unicorn?