What is the most useful-to-HN-method to remove the derailment attempts?
Downvote, flag, move on?
I just wish there were more effective tools across the web, (i.e. not just HN) to tackle the people who are trying to cause division by derailing threads with argumentative comments.
Yup, and in egregious cases, email hn@ycombinator.com. The latter has the downside that it depends on how online we happen to be, but the upside of guaranteed message delivery. If the email is short and includes a link and a brief statement of what's being reported, it's often easy to do something quickly, even if it takes us (er, me) longer to reply.
Downvote, flag, move on?
I just wish there were more effective tools across the web, (i.e. not just HN) to tackle the people who are trying to cause division by derailing threads with argumentative comments.