It seems that the human concept of God from most religions always included a principle of punishment for wrongs. No religion ever thought of a God of grace and unlimited love as expressed in the gospel of Christ, until Christ came. Therefore we do not find significant opposition to God's justice and anger (deemed as cruelty) except as a result of a world view born from gospel influences. The first to famously accuse the God of the Old Testament of cruelty was Marcion.
Marcions believed in two God's the Old Testament one and the New Testament one. He thought the Old Testament one was inferior, cruel and jealous.
The basic rebuttal to the accusation of God as being cruel was made by Tertullian by making fun of a God imagined by Marcion who was irrationally good but not just. In other words even weak men understand that there must be punishment for some crimes, so what kind of pathetic weak God would not punish evil men?
But it is here sufficient that the extreme perversity of their god is proved from the mere exposition of his lonely goodness, in which they refuse to ascribe to him such emotions of mind as they censure in the Creator. Now, if he is susceptible of no feeling of rivalry, or anger, or damage, or injury, as one who refrains from exercising judicial power, I cannot tell how any system of discipline—and that, too, a plenary one—can be consistent in him. For how is it possible that he should issue commands, if he does not mean to execute them; or forbid sins, if he intends not to punish them, but rather to decline the functions of the judge, as being a stranger to all notions of severity and judicial chastisement? For why does he forbid the commission of that which he punishes not when perpetrated? (Tertullian 11.1.26, THE ANTE-NICENE FATHERS translations of The Writings of the Fathers down to a.d. 325 THE REV. ALEXANDER ROBERTS)
The simple argument against those who accuse God of being cruel prior to the giving of his own Son for the salvation of sinners wish for only a loving God that does not punish and is not offended. This is similar to thinking that Santa Claus would be suitable for a career as a general in a world war. Human's are not loving and when they accuse God of cruelty it is merely a denial of justice and their own sinfulness.