DDoS-for-sale sites are not "free speech sites", they are for-profit criminal organizations engaging in the violent censorship of people that are too poor to afford proper DDoS mitigation or that want to control the privacy of their users by managing the SSL certs.
The booters aren't usually as powerful as these 600Gbps+ monsters, but they're quite adequate to wreck almost any network for a long time (most IP transit hookups for racks are 10Gbps or less, these attacks can be well in excess of 100Gbps), requiring you to spend exorbitant amounts of money to protect your site against what are essentially bored high schoolers with a spare $20, your competitors, or whomever. That money is then dumped back into the system, allowing the attackers to build even more sophisticated and powerful infrastructure, leading to worse attacks like the ones we're now starting to see. Krebs was one of the people to document this trend, and now his site has been censored off the net by the same people he was writing about. Why is it so surprising to everyone that he's avoiding Cloudflare?
Search Google? So should Google be delisting these sites?
I recognize that it's impossible to eradicate the problem 100%, but by driving it underground, you can dramatically reduce the amount of it by making it harder for them to conduct their business. Cloudflare could do this in a day if they wanted to, instead they sit behind a "free speech" argument waiting for someone to force them to cut it out. Don't say I didn't warn you if the government comes in to change the liability laws to prevent this sort of behavior in the future. Nobody's going to defend DDoS spam packets from criminal botnets as "free speech" when they're preventing all speech from occurring.
With or without Cloudflare in the mix, how the heck would you go about making the connection between a flood of traffic from a large number of IPs, and any particular booter site? I don't understand how taking Cloudflare out of the mix helps you stop the DDoS.
As an aside, the FBI is indeed interested in investigating large DDoS attacks. Contact your local field office to see if yours qualifies! :-)