The word "precious" has two definitions. The more common one is "closely held, of great value". The other is "fussy". You've hit the second definition square on the nose.

I really don't like Shrek.

Fair enough. If my nom de plume rhymed with something, I would probably get tired of it too.

I see behind the screenwriting and see a VERY calculated fairy tale

I hate to break it to you, but all fairy tales are calculated. They are pedagogical tools, from the very earliest times.

designed to appeal to those with underclass ambitions

The underclass, as you so overclassly call people, are entitled to ambitions.

If you imply that people have ambitions to become the underclass, you had better find out what people have been slipping into your bottled water. Even urban music, which makes its producers so much money, is steeped in violence and despair. To articulate a cultural problem is not to aspire to it.

and who applaud the tearing down of traditional values.

Puleeze. Where would America be if the "traditional values" folks (also known as "Tories") had carried the day from those down-tearing Sons of Liberty? Tearing down traditional values is one of the things America does best. Anything worthwhile reappears based on its true value, rather than the value it derives from tradition.

The glorification of farting and mediocrity,

Shrek exhibits intelligence, loyalty and honor. Fiona exhibits good sense and self-knowledge. Donkey exhibits discretion and understanding. The characters all have their faults, but their better selves win the day. I'll take that mediocrity, thank you.

Regarding your horror of farting, I urge you to avoid the mediocre comedies of Aristophanes, Plautus and Shakespeare, the mediocre essays of Montaigne, and the mediocre poetry of Chaucer.

the elimination of beauty

If we are wise, we know that physical beauty is a subjective thing, and varies from era to era and place to place, and furthermore, is only skin-deep. I understand you might find plump green people unattractive. I've seen your drawings of that emaciated blonde creature with the impossible physical proportions. Bazooka Barbie, anyone?

or of speaking properly

Are you talking about Shrek's Scottish burr, or Donkey's American South twang? Fiona speaks standard American English, which could be considered rather, um, provincial if you were from the British upper classes. The grammar is, overall, not bad. I have no quarrel with the occasional "ain't" or double negative: I can read Twain without cringing.

is fine for the uneducated children but for adults with a brain its pure poison.

Now, if one were really concerned about cultural degradation, that sentiment, ill-founded as it is, would be completely reversed. But if the adult were a snob, of course the characters in Shrek would be poisonous. Heaven help us that people who are pudgy and speak with strange accents and dress unfashionably might be considered heroic. We would have to look beyond our mirrors to discover our value!