2. That’s it. There is no other way. Whether it’s Earnest Engagement or Immediate Witty Rejoinders (that in most cases are not witty), responding to trolling is essentially indistinguishable from trolling. Admittedly, there are always marginal cases where it’s not immediately obvious that someone is a troll, but here’s a protip: if someone announces that African-Americans are genetically inferior, they’re a troll.
Also, you’ll notice the “minus” sign in the graphic above, which is very useful. If a troll and one or more Earnest Engagers are involved in a circle-jerk, collapsing the thread allows you to immediately move on to something that isn’t necessarily wasting everyone else’s time with a minimum of scrolling. Oh, and active moderation by the site owners is Never Happening for Obvious Reasons, and please don’t use this theoretical possibility to defend the behavior of (in ascending order of responsibility) trolls and people who engage with repetitive trolls.