Why is Mr Horton such a fan favorite?

I don't think the OP meant it in that way. He/she seemed to be questioning WHY it was such a popular episode (and it was - 'Peter' on "Family Guy," you know, the cartoon, made a reference to that episode!!). Now If something like that makes it to "Family Guy" or the like, you KNOW that prob 80% of the audience 'get' it, so it's obviously a fan favorite. Now, what I wonder is why you're interpreting that to mean that the fans (or the OP specifically) LIKE the character, who was a pedophile?? Ummm, that's not the case here (at least in 99% of those who talk about the episode). I don't know how old you are and whether or not you watched DS in its original run, but very few shows during that time touched that issue; thus, making it an episode that people were INTERESTED IN. That's human nature - it doesn't mean that they 'like' the character, Mr. Horton or was 'turned on' by the thought of Arnold and Dudley in nude photos (yikes).

Seriously, if you don't understand why this would be of interest to viewers, esp since many children ARE victims of sexual abuse (though usually by those closer to the home), than you're the one who may not be thinking very clearly. Don't be so quick to judge - it's normal that kids would be interested in this topic (and I happen to be a clinical social worker who does child and adult therapy). But perhaps it hit a sensitive spot with you, so I'm not going to stoop to your level, esp. because I'm writing this with my 'therapist's cap' on.