These are separate issues. From the perspective of a social network operator who is interested in personalized data to collect an accurate social graph and ult

These are separate issues. From the perspective of a social network operator who is interested in personalized data to collect an accurate social graph and ultimately sell ads (or data), spam accounts are arguably more of a threat than trolls, as spam accounts will never exhibit 'normal human' behavior like providing truthful data about their lives or presenting a truthful network of influence. Troll accounts may in fact promote more engagement (in the most clinical definition of the word), since both trolls and their victims are actual humans. But being harassed drives people away so it isn't just a user retention risk, but also a reputational one. Outside of social networks, a frequent solution to curb harassment is community moderation like downvotes, which only works if the majority is on the side of the victim and not the attacker. When no such consensus exists, all involved parties will be in disagreement with the opposing side, and any administrative to adjudicate a decision on who's in the right will wrong at least half of the participants. ML may be able to filter out blatantly spammy content, but moderating adversarial content is something us humans haven't quite solved either.