That "undeputized publicist" thing is really interesting... with some quick thought on the matter I personally think it rather foolish. It assumes that a "fan" would intentionally use the characters in a malevolent or unfit manner, perhaps even with regard to larger social norms, which seems to run contrary to the intentions of most fans, although there is always the possibility of such misuse... but this is not just limited to "fans."
And that's the point, isn't it? They can't tell if someone's Scarlet Witch porn (look, I'm just gonna come out and say it: Mess with the ears all they want, she's still dressed as a Playboy Bunny) is a tribute, parody, or attack, without investigation. They also don't have time to read every bit of fan fiction to make sure it doesn't veer into gross mischaracterization.
In principle, I agree with you, really, but I also see why the companies can't agree without doing themselves harm.
That their own writers are worse is irrelevent...
When one considers the matter further, it is based on the assumption that the holder of a copyright or trademark of a fictitious character "knows" what is right for society at large with regard to the use of said character. But in my opinion this is false... unless of course they are the original creator of the character in question.
My thinking on the issue is that, rather than "property," copyright is more like a (temporary, in theory) monopoly on distribution and trademark is more like identity.
For copyright, the bargain is that creators donate to the public domain without needing to find patronage in exchange for the right to determine how and when the thing is released for a while. (I think that speaks to your censorship issue--it IS censorship in a way, but it's supposed to be temporary.)
In the case of trademarks, I can see it being touchier. The law is messier in this regard, but when you think of it as part of corporate identity, it'd be like someone using your e-mail address or a picture of you in a brochure. Allowing it basically puts everybody's reputation into the hands of the unwashed masses.
And to claim otherwise on these grounds smacks of censorship in the form of a stifling of freedom of expression... and in my opinion is very dangerous to our democratic foundations. What would be next? Marvel disagrees with a critic of the Spider-Man comic and sues for slander or defamation of character?
That's sort of ironic, since the last time someone did that, the solution in the industry was censorship...but of their own work, not that of the critic (the Comics Code). However, criticism is also covered by Fair Use, so you can't go after them for any such thing.
Again, this is with regard to non-profit use of a character only. People should have the right to creatively express themselves with the existing characters if there is no material gain in the activity... and furthermore, they shouldn't be held accountable if they succeed in popularizing a character, that to me only means the "owners" have done a disservice in their use and interpretation. Of course, if there is a really egregious misuse, then of course I feel they have the right to take some form of action... but that should be on a case by case basis.
Which isn't too far off the reality, as I understand it. The problem is the concept of "dilution of trademark," which says that the concept (a brand name like "Kleenex," "Xerox," or "Google") has become so commonly misrepresented as to be useless.
So, if Disney doesn't at least contact and (I'm guessing) get some sort of liability disclaimer from every bakery who sell Pluto-decorated cakes, someone far less scrupulous can claim dilution of trademark and use the image for...less friendly purposes.
But as I understand it, most of the people hit with Cease and Desist orders usually don't suffer any more harm than, y'know, a load of laundry. Normally, if it's not a sales thing, they're more likely to get a contract in the mail that allows them to use the image for that specific purpose.
A few years back, Marvel tried to solve this problem by creating an online license
Again, I think in the case of non-profit "fan" use it's silly and time consuming... unless there's a really egregious misuse of a character.
I give them credit for at least acknowledging the issue and offering a cooperative way out of it. If it had caught on, they could be fairly liberal with their policies (and friendly to their customers) without losing any of their rights. And they don't need to look like jerks by stomping on twelve-year-olds using a Wolverine-like character in an online video game (which they've done...repeatedly).
But I guess what we have right now is a "don't ask, don't tell" type of thing regarding this matter... at least until someone foolishly or unintentionally presses the issue. Which I am NOT inclined to do... just in case anyone out there is seriously listening to our conversation. 
All I ever wanted was to have fun... I think that's what comics should be about right?
Didn't Dan Didio actually say (a few years back) that comic fans aren't interested in fun anymore? He meant humor titles, but the statement out of context explains so much of the last twenty years or so...
