Psalm 12 is the likely basis for this belief; you have cited it yourself. Here is what the KJV of these verses actually say:
[SUP]6 [/SUP]The words of the Lord are pure words: as silver tried in a furnace of earth, purified seven times.
[SUP]7 [/SUP]Thou shalt keep them, O Lord, thou shalt preserve them from this generation for ever.
Sound understanding of scriptural truth begins with careful reading of Scripture. The Scripture does not say that God will preserve His word for all generations. Rather, and in complete refutation of your assertion, it promises that God will preserve His word from an evil generation!
Others have presented evidence that verse 7 refers to the people of God, rather than to His word. Every other use but three of "preserve" (and cognates) refers to people (two cases address wine; one case addresses knowledge). I encourage you to rethink your position on this matter.
The chapter is a contrast between David's love of God's words and the vanity of men's words. Incorrectly reading verse 7 to refer to a promise to preserve the poor forever ruins the praise of God's promises David is offering. It also leaves us with the strange, indefensible position that God is promising the preservation of the poor in always -- a doctrine not to be found elsewhere in Scripture. It also contradicts the very first verse, where David states that "for the godly man ceaseth; for the faithful fail from among the children of men." If we are to accept the reading (Kutilek and others) offer we must conclude that the "godly man" and "faithful" can not also be "poor" and that, oddly, the poor are therefore ungodly, faithless, and will be preserved forever.
A quote from Spurgeon:
“What a contrast between the vain words of man, and the pure words of Jehovah. Man's words are yea and nay, but the Lord's promises are yea and amen. For truth, certainty, holiness, faithfulness, the words of the Lord are pure as well-refined silver. In the original there is an allusion to the most severely-purifying process known to the ancients, through which silver was passed when the greatest possible purity was desired; the dross was all consumed, and only the bright and precious metal remained; so clear and free from all alloy of error or unfaithfulness is the book of the words of the Lord. The Bible has passed through the furnace of persecution, literary criticism, philosophic doubt, and scientific discovery, and has lost nothing but those human interpretations which clung to it as alloy to precious ore. The experience of saints has tried it in every conceivable manner, but not a single doctrine or promise has been consumed in the most excessive heat. What God's words are, the words of his children should be.”