Cloudflare realizes that the status quo makes it hard to prove standing to sue, and that's a large part of what allows them to get away with it. But if you go to Google right now and search (
https://www.google.com/#q=ddos+booter), you will find that basically all of them are behind Cloudflare. They have spent an enormous amount of time brainwashing Silicon Valley into thinking that this is a free speech argument (as evidenced by some of the absolutely ridiculous comments in here comparing DDoS attackers to unpopular speech protection or making absolutely shameless comparisons to whistleblowers like Aaron Swartz).
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?