Well technically an author, too, isn't allowed to scrape content from CL. Just like an author of a book is not authorized to make a copy of his own book. Can't break publisher's rules.

It is just that, with a copy-paste job, it would be impossible to detect this, which is why they seem functionally equivalent. But actually they're not.

Also automation and convenience have huge legal implications. I can, for example buy an iPod in the US and gift it to a friend of mine in Turkey. We have effectively circumvented state tax. I can't, however, write a website that acts as a broker between US passengers landing in Istanbul airport, and people who want cheap iPods. Even though they would be technically paired up with a "friend" and would be within their legal rights to bring valuable goods into the country.

I can have a friend stay a few days at my house, but I can't turn my house into a hotel with Airbnb. Volume and convenience affect the bottom line for different parties.