As a "healthy version of a nostalgiatard" myself I can't agree more about The Dark Crystal! ^^
*to clarify, I'm aware I'm a ridiculously big fan of it, yet that won't stop me from noticing and acknowledging it's flaws, and understanding not all people will see/appreciate it in the same way or sense I do *

Luckily we have a small community of fans here at DA who get along well and are creative and kind people...yet yes, I've stumbled onto some folks who are into it which couldn't do less but making any rational person cringe.

I would  take it as "okay" if T.D.C. happens to be their "precious childhood memory" and they think anything off-canon or anything which doesn't match their views on it is "wrong" (since I go all for tollerance on different points of view and that's quite how I roll : I love expanded and tweaked AU's about it *if they're well done or course* but if these ther fans  don't, I do understand and respect that)
Now--when it comes to whitstand their  moaning and ranting about what they don't like on other people's AU'S " because something's off-canon/ because not everything's just like in the movie/ because added new non-canon characters/ because some reversioned situations/ because smex / because darkness, etc" it really annoys me.
If such nostalgiatards could debate in civilized terms with their friends or with like minded people on what -and why- they hated so much, OR  ask politely (may I remark politely?) about the choices of an artist/writer on why they did a certain thing about TDC which they don't agree with- if they really feel they must "say something about it"- I'd say that's all fine- Especially if they see things very differently and don't agree with what one wrote/drew or genuinely can't understand it...

But that's almost impossible or at least very unlikely to happen XP.  
The most usual confrontation happens when you get commented over a thousand times by one of them demanding "why did you do such a horrible thing? or saying "you should be sued by the Hensons and Froud and burned by the holy inquisition for drawing that!" XD...*Been there, really!*

All I can say is, even being a huge fan, I feel embarrassed by those who- beyond what they may like or dislike from Au's and fan-interpretations of TDC- come off as agressive, despindent, outright disrepectful and even violent towards any other fa or non fan who did anything they don't agree with.

If only  all fandoms had more people as kind, supportive  and civil regarding differences as some  worthy , healthy fans I know at part of the D.A. TDC community, things would be much better!