Um, yes they can. You are free to post the same content elsewhere -- you still have copyright in the material. What you don't have is rights to redistribute content from Craigslist. The publisher's rights (which you granted) are different from the author's rights, but they still exist. That doesn't make them liable for your content.
What's the difference between copying and pasting from a single text file to both CL and krrb and copying and pasting from a CL post that you wrote to krrb? They're functionally equivalent as you're the author and retain your authorly rights in either case.
The krrb tool extracts data from a file not on craigslist servers, but from the browser cache on your own computer. It's a browser plug-in, not a server-side tool. If CL is okay with you downloading a copy so that you can see the post that you just made (which they obviously are by virtue of how their service works) then in fact there is no additional bandwidth being consumed!
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.
It's not merely "the same content", it is content automatically sourced from Craigslist, and while that may seem like a picayune distinction, it is not.
It's not automatic. A user has to click a button on his bookmark bar for it to happen.
CL seems to have a stone age version of automatic. A cave man would think a cigarette lighter automatically creates fire, but it just technology that's improved.
Instead of rubbing sticks together for a half hour we can make fire with flick of our thumb. We still had to do something.
Higher productivity != automation and shouldn't be used as an arbitrary measure of legality.
