Obsession is not interest in extreme form.
Obsession is a relation of a mind and its (beseiging) object. Interest is inter-esse: between-being, starting with mind and moving toward being explicity understood as beyond one’s mind. In other words, obsession is strictly immanent and interest is transcendent. I think celebrities understand best the impersonality of a fan’s obsession: next year it will be some other object, with no remnant of last year’s fixation. Genuine interest leads a person to new understandings in pursuit of understanding, and this changes a person in profound and elusive ways. Obsession leaves an obsessive pristinely unaffected by the (non)encounter. Obsession is a hermetically sealed self-protective wall of passion.
The distinction between interest and obsession is analagous to that which separates religion from fundamentalism. It appears to be obsession with God, but it is in fact a mere obsession with one’s own manmade god-object, and its effect is one of isolation from what lives beyond one’s own mind and mind-objects. It is an immanent notion of transcendence, not an active relationship with what can and will defy it (often via transcendence’s #1 favorite agent, that clueless asshole next door).
Here again, the supposed “extreme” is not something gone to far, but rather a fiery counterfeit — a self-protective wall of passion.
This is why I keep insisting that fundamentalists are not religous extremists at all but antireligious ideology worshipers, or to say it in their own language, idolators. (The idol is a theology, an ideational image of God confused with God.)
Instead of deciding whether or not to accept this view, instead just try it out: Next time you see fundamentalists (and it doesn’t matter what denomination of fundamentalism it is) freaking out about words, definitions, codes, symbols and ideas in their heads, and treating them as more real and important than real human beings living real lives — just try thinking of them as irreligious obsessives who haven’t the slightest clue of what transcendence is, nor, consequently, what religion is, fear transcendence like eternal death, and hate every spark of living evidence that transcendence is real, most of all those who see things differently.