"What is true for you today may not be true for you tomorrow."

I, for one, am totally fine with that - in fact, it is what I hope for. It is my hope that humans will learn from past mistakes, gain greater understanding through experiences and science, through contact with one another and the sharing/exploration of ideas. If one is open to learning, that learning can influence & encourage change and the shedding of mistaken ideas. Never fear being wrong, because if you are willing to acknowledge you were wrong, you have learned and thus gained.

Change = growth. No change = stagnation.

"No human standard—no person, no group of people, no document—is [then] immune to challenge.”

As it should be. Challenge everything, test it, push hard to see where it's exploration leads you. Just because something was accepted as true and worthy in the past doesn't mean it MUST be true and worthy today or even in the future. Life, growth, learning are not stagnant. Death is.

"if we remove the notion of the creator God, who, by the nature of his being, establishes the framework of morality and of human existence, then nothing will be able to stand up to challenge."

That's just ridiculous. Common sense, risk vs reward, harm vs nuturing, education, life experiences. . . all of these things and more can be used to meet challenges. We are not without resources to figure things out.

Whether god given or the results of evolution, humans have a brain and they have a heart - use them. They are good tools to use to make decisions, both moral and practical. Oh sometimes we will struggle looking for answers (maybe even often), sometimes we will make mistakes through ignorance or the lack of foresight, sometimes we will behave selfishly and callously, sometimes we will be confused - but they are all part of the learning process.

At some point, humans must grow up, leave the nest, and figure out life for themselves. Experience is the difference between knowledge and wisdom. It has its risks but it has its rewards. We should never stop trying. Persistence often pays off.