Usual US answer is: “mentally ill individual acting alone”. Thankfully, silent conspiracy believing is still relatively uncommon in the mainstream USA.
We search for one individual. Find individual. Individual gets face in news.
“Must have been something in his childhood”
Then, we forget.
Thing is though, these are all “has-beens”. In 2015, they were important. In 2018, they are generally seen as “old news”.
Indeed. What makes it difficult is conspiracy people get their ideas from other conspiracy people. Without “reality checks” now and again, they descend so deep that they live in an alternate fantasy world. It’s sad really for most, and dangerous for some.