Kragen seems to be suggesting a parallel, not an alternative. If you are strongly attuned to something, the same mechanism that would amplify these thoughts when they occur spontaneously would also presumably extend to reading spurious "deeper meanings" into the actions of others.

That's right, and in the case of memetic contagion, the attunement can be an emergent collective phenomenon rather than just an individual preoccupation.

I think the nature of intrusive thoughts is a bit different from memes or other contagious ideas. Intrusive thoughts are persistent in part because of the "semi" paradox required to ensure you're avoiding a thought. eg, in order to not think of a pink elephant, some process in your brain must be checking for a pink elephant. This process is by some definition thinking of a pink elephant. People who are more prone to OCD-like thinking will obviously have even more trouble with this task, since they are less successful at terminating a train of thought than the average person.

In the sort of memes you're describing people are actively doing their best to (sometimes falsely) find dog whistles, or secret CIA involvement. The emotional rush that comes from suspicion or outrage is wholly different than someone with OCD failing to terminate a train of thought.