From the screenshots given, setro never threatened to DDoS anyone. He stated that he believes hammerhost deserves to be DDoSed, but he wasn't going to do it. People are interpreting this statement as a threat.
A cop who arrests a murderer can believe that he deserves to be put to death, but that doesn't mean he is threatening to do it.
If you think that Setro is threatening to DDoS HammerHost, you're interpreting it incorrectly. If he wanted to do it, he probably already would have. The topic of DDoSing was brought up when Ravencroft and Setro got into an argument. Why would he all of a sudden threaten to DDoS HammerHost just because of an argument with someone that has nothing to do with HammerHost? I 100% believe that Setro would like HammerHost to be DDoS'd, but this doesn't mean he will.
If he says he doesn't regret attacking a hosting service before
Setro had nothing against CBM Hosting, he had something against Ravencroft. He says he doesn't regret DDoS'ing Ravencroft.
who's to say he won't attack hammer's service?
This is just speculation. We can speculate all day about what Setro might do, but if he clearly states that he won't DDoS HammerHost, that's all we have to go off of.