For me, words are judged by two criteria: beauty and precision.
Most of us know that there are certain words and combinations of words which are extremely (almost ineffably) beautiful to the ear. For instance, my favorite word is silver; I find most tree names lovely as well: ash, poplar, beech, brich, elm. This is not because of something in their meaning, although I like silver and most trees quite a bit, but simply for the pleasant sound that they make when spoken or read. Like Lord Peter Wimsey, I find it very easy to be drunk on words, just the sounds of them. If, as is proposed, language is reduced to the lowest common denominator, all beauty is ruthlessly stripped from it. No more Shakespeare, no more John Donne, no more King James Version, no more Dylan Thomas, or Gerard Manley Hopkins, or Tolkien (perhaps especially him because of his love of the archaic) or even e.e. cummings. Even if their works were "translated" into a more "acceptable" form they would not--could not--survive because they would not remain themselves.
This is partly because the precision of them would be gone. Take, for instance, the last line of Manley Hopkins' "The Windhover":
and gash gold-vermilion.
Nothing terribly difficult about that--gash, perhaps--except for vermillion. That's simple enough to fix. Vermillion is just a sort of red. So, stick red in and there you are:
and gash gold-red.
Or there you aren't. Because, aside from completely and utterly destroying the rhyme and meter, the precision of the sentence is lost. Red is a broad word--it is quite likely that someone reading the amended sentence would think of a glorious rich, dark red; a very lovely color to be sure, but not the intense orange red that is vermillion and so not the right word. To reduce language to the lowest common denominator is to lose the ability to communicate accurately.
Words matter. Theologically speaking, the changing of one word or part of a word can very easily mean the difference between right belief and heresy. Thus, it is the difference in 'Theotokos' and 'Christotokos' which separates the position of the true church from the Nestorians. King Solomon, all those thousands of years ago, knew that words have power for "a word fitly [my emphasis] spoken is like apples of gold in pictures of silver." We cannot take lightly any attempt to wrest them from us.
The Deputy Headmistress brought up a comment which posited a sort of conspiracy theory. I agree with her that it is probably overstating the case, but this sort of idea about language is indicative of a mindset which is deeply disturbing; one which desires, consciously or unconsciously, a dumbing down of the general populace and a lack of independent thinking.
Just because I'm feeling protective of my words, here's the full text of "The Windhover." Hey, they'd even have to change the title of that one! It's full of lovely words.
I caught this morning morning's minion, king-
dom of daylight's dauphin, dapple-dawn-drawn Falcon, in his riding
Of the rolling level underneath him steady air, and striding
High there, how he rung upon the rein of a wimpling wing
In his ecstasy! then off, off forth on a swing,
As a skate's heel sweeps smooth on a bow-bend: the hurl and gliding
Rebuffed the big wind. My heart in hiding
Stirred for a bird,--the achieve of, the mastery of the thing!
Brute beauty and valour and act, oh, air, pride, plume, here
Buckle! AND the fire that breaks from thee then, a billion
Times told lovelier, more dangerous, O my chevalier!
No wonder of it: sheer plod makes plough down sillion
Shine, and blue-bleak embers, ah my dear,
Fall, gall themselves, and gash gold-vermilion.
~Gerard Manley Hopkins