We also get into trouble when we take a couple of verses out of the context of the larger statement...
"12 Help, Lord; for the godly man ceaseth; for the faithful fail from among the children of men.
2 They speak vanity every one with his neighbour: with flattering lips and with a double heart do they speak.
3 The Lord shall cut off all flattering lips, and the tongue that speaketh proud things:
4 Who have said, With our tongue will we prevail; our lips are our own: who is lord over us?
5 For the oppression of the poor, for the sighing of the needy, now will I arise, saith the Lord; I will set him in safety from him that puffeth at him.
6 The words of the Lord are pure words: as silver tried in a furnace of earth, purified seven times.
7 Thou shalt keep them, O Lord, thou shalt preserve them from this generation for ever.
8 The wicked walk on every side, when the vilest men are exalted."
Just as we learned to diagram sentences in English class, If you read the whole chapter. In this case we see that God is protecting the poor and the needy, the verse 6 is about God's words being pure and we can trust His commitment to the poor and the needy. In verse 7, it is a statement that God will preserve these people. It isn't God's Word that He has promised to preserve... it's people.
As is often the case between opposed sides all over TOL; as is thus far the case once more on both sides of that debate; as is the case in your above post: each ends up illustrating once more the myopia that attempting to prove a view right or wrong often results in.
For example, you assert "It isn't God's Word that He has promised to preserve... it's people."
You were able to arrive at that conclusion as a result of what?
Of having those passages from which to conclude what you have.
In other words, there they are; still around after all these centuries.
Whatever that means, or implies, one thing is obvious; somehow those passages ended up still being around a bit longer than the time in which they were written.
I'm assuming those words in that chapter had been meant towards encouragement "from this generation for ever."
How would they know that without those words?
Would there even be "a debate" had no Scripture "survived" to begin with?
Those are questions each individual has to ask - questions few appear to. And the more dogmatic the individual, the less they are likely to. All such ever conclude is that to ask such questions to begin with, is to go against their version of "the truth" that one is "being divisive." Myopia on myopia.
At some point; one has to break oneself free from the ill-advised habit of looking at a thing towards proving it either right or wrong, and just look at it to what actually doing so objectively might actually involve; ever aware that tomorrow one may see things in a different light altogether.
If there are no holes in my own argument, I will be very surprised. One must look for the holes in one's own view - constantly.