Could there be any possible action proving Yahweh to be cruel?

Google gave the following definition for mercy:

Compassion or forgiveness shown toward someone whom it is within one's power to punish or harm

Excluding the concept of sin excludes the concept of mercy with respect to compassion or forgiveness and punishment.

If one assumes that God is the most powerful being, the fact that the world does not seem to be as bad as it could be would seem to imply some degree of either compassion or apathy (i.e., the power to harm would have presented opportunities which do not seem to have been taken).

Excluding eternal aspects, particularly "the chief end of man . . . is to glorify God and enjoy him forever", and expecting to perceive God as merciful would be like excluding concepts of vitamins, fiber, etc. (or even agreeing on what good health is) and expecting to perceive a nutritionist's advice as being in one's best interest--good tasting is more "real" than nutritionally good. (Christians would claim good effects from God, much as one who follows a nutritionist's advice would claim good effects; but unlike the nutritionist example one cannot have a "there is no God" control group for scientific testing of God's general mercy. Also, as the Apostle Paul states [1 Corinthians 15:19]: "If only for this life we have hope in Christ, we are to be pitied more than all men."[NIV])

Another way to look at this, and I think the one that makes the most sense, is that God is in His very nature who He is, and we get our definition of "good" from this. I think the difference between this derived definition of good based on God's nature, and God just possessing the quality of "goodness" (and like qualities, mercy, holiness, etc), is best shown through a good ol' fashioned proof by contradiction.

Proof:

1. Assume God possesses the characteristic of "goodness."
2. This means that God is conforming to some higher law of what is right and wrong.
3. Therefore God is not the highest authority, for even He must conform to something higher.

Therefore, God must be "goodness" itself. His very nature must define what the word means. He certainly has shown that he has the authority to say what is good and what is not (Genesis 1).

With this definition in mind, we can see that God indeed can do whatever He wants because His will is not bound by anyone or anything else as we see in Daniel 4:35:

“And all the inhabitants of the earth are accounted as nothing, but He does according to His will in the host of heaven and among the inhabitants of earth; and no one can ward off His hand or say to Him, ‘What hast Thou done?’”

We can further see that while God can do whatever He wants, He is still completely good, because what He wants becomes what goodness is. The good news for us is that God loves us and does not change (The definition of goodness and the fact that He loves us never changes):

For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life. -John 3:16

And:

Jesus Christ is the same yesterday and today and forever. -Hebrews 13:8

Running with this idea, if He were to commit an act that was not merciful (and thus not good if for no other reason than He lied about His mercifulness) then He would not be merely breaking some higher "rule," but in essence He would have denied His very nature. This, according to common sense and (above all) scripture, is impossible.

If we are faithless, He remains faithful; He cannot deny Himself. -2 Timothy 2:13

Mercy is when judgment is withheld from those who deserve it. God is merciful in that He oftentimes does withhold judgment and punishment from those who deserve it.

However, God is not merciful in every situation. If that were the case, He no one would ever suffer any penalty for anything they ever did. Hitler and Stalin would be completely without judgment. This is not the case.

There is a distinction between God being Love and God being loving. God is love in that love is an attribute of God. Loving describes His actions. God is merciful (adjective), but God is not mercy.

Regarding the death of Christians, history is full of Christians who have died young and who have been killed for their faith. Yet, in the truest sense, God was merciful to them--not in preventing all harm and death from them, but in forgiving them for their sins against God. Death is the fate of all men, but death is not the end. Mercy has to do with our sins being forgiven--not in us being freed from all suffering.