"It is Christians who characterize God as all-loving"
To be fair, it's the Bible that first characterizes God as all-loving. John the Apostle says "God is love." So, yes, Christians have that view of God based on biblical teaching.
"If Christians claim that God's mind is beyond our understanding, and therefore refrain from describing God in moral terms (loving, kind, patient, etc.), you would then be justified to criticize atheists in the way your article does."
First, I don't accept the either-or you are setting up. You don't have to know everything about a person in order to have a general or basic understanding of that person's nature or character. We know what God has revealed. We can't know more than that. But we can know what has been revealed.
Second, my article is responding specifically to this assertion: “A loving omnipotent god able to see the future would have made better humans even WITH free will." Even if I grant some of what you are saying, that doesn't mean we can make all the assumptions which are inherent in this claim.
"Is there anything that God could do that would be contrary to His nature as you understand it?"
I do not believe it is possible for God to act against His nature. But if you mean... Can I imagine an act or deed that would be contrary to God's nature? Sure.
But...and there is a "but"...
If God meets fallen, sinful, messy humans where they are at, is that God coming to where we are and communicating with us in ways we understand OR is that God sinning?
That's where a lot of the "rub" lies, especailly when it comes to the Old Testament. To understand that, I refer you (and others observing this) to "Is God a Moral Monster?" by Paul Copan.
It IS fair for an atheist to say: "You know, when I hear how Christians describe God, I don't see that always in the Old Testament. It strikes me as inconsistent and troubling."
Okay, that's fair. And we can have that discussion. I'm not faulting you or anyone for putting that on the table. No problem. Totally legit.
What I object to is threefold:
a) Declaring with certainty that you know what God would do or wouldn't do
b) Evaluating God based on a surface-level reading of the Bible and an emotional reaction to it. And not taking into account all that the Bible says about God. For example, the Bible presnts God as all-knowing. An all-knowing God is a qualified Judge. Such a Judge can't be fooled, deceived, or be ingorant. Such a Judge would know ALL the thoughts AND all the actions of every person He judges. That has to be taken into account. Otherwise, it's not a fair evaluation.
c) Judging God based on an ill-defined or subjective moral standard. If there is no God, then what is the objective, moral standard that atheists seek to judge God? or anyone?