The fanfic authors have a great INTEREST in the creations. "respect" depends on many things. I have much more respect for an author that recognizes that their creations are going to spark other ideas in people, and that some of those ideas will be ones that they think are stupid, offensive, sick, or just WRONG, and that there's NOT ONE DAMN THING they can do about it. And that most of those people are also the ones who might be buying their books.
I think a lot of fanfic is stupd, sick, etc., all of the above. OTOH, I think the same about some published/aired material. Many Fic writers think that they have good ideas; on occasion, they may even think they have a BETTER idea than the real author. On some occasions, they're probably right.
But if applied strictly, according to the statutes as quoted, MOST MATERIAL PUBLISHED TODAY WOULD NOT BE PUBLISHABLE. All you authors out there screaming about how the protection needs to be enforced -- it's a good thing Disney didn't exist a few centuries back. How many people have ripped off Shakespeare -- shamelessly, without respect for what the author might have wanted, etc? Well, that's okay, because HE isn't copyrighted or trademarked. You don't need to respect anyone if they don't have the law on their side, right?
And as to law... how many of you out there drive at or below the speed limit? REALLY? None of you going 45 in a 40, 65 in a 55? If you're so law-abiding, I sure hope you could honestly answer "yes, I really do" to that question, because you're about as likely to be causing damage to others and society that way as you are by fanfic -- more so, probably, since I never heard of someone losing control of their fic and killing a bunch of people. And you're violating the law just as absolutely, clearly, and for the same reasons: because a lot of other people are doing it, you think it's okay, and most of the time no one cares.
As to not understanding the people who write it -- I suspect a similar percentage of people would be hard put to answer "no" to the question "so, you've NEVER speculated about anything having to do with a TV show? Never fantasized about inserting yourself into a situation -- maybe with that "hot" star character? Never wondered what would happen if X (from show 1) met Y(from show 2)? Never wondered how hero A might deal with situation B? Never had an idea for an episode you'd like to see?"
All those reasons drive fic writers. They just get off their metaphorical butts and actually write it instead of thinking about it idly. They're a tad more interested, a bit more motivated, or maybe just like writing.
Sure, the law says you can't do it. There's a lot of laws that are either too broad or too vague, or that if applied strictly would be too limiting. In the case of current intellectual property law, it's also relying on the fact that a large body of prior work is ALREADY public domain and can be drawn upon. But with current trends, nothing is likely to EVER enter public domain again unless explicitly placed there, and it's that kind of thing that drives the production of new material. We build on the old stuff, but if the old stuff is surrounded with guns and electrified fences saying "Do Not Touch!!" we get more reluctant to try. Fanfics are part and parcel of the current-world writing environment. You don't have to BE a fic writer, but don't be a twit about them either.