How can one respond to those who describe God as sadistic and as loving to torture people?

This statement is a lie and a slander against Allah, Exalted and Sanctified be He. He does not love to torment His creation; rather, He loves their mercy and guidance. He is more merciful to them than they are to themselves or their mothers. Allah, Exalted be He, has informed us of His perfect richness, mercy, and benevolence, saying: ﴿WHAT WOULD ALLAH ACCOMPLISH BY YOUR PUNISHMENT IF YOU ARE GRATEFUL AND BELIEVE? AND ALLAH IS EVER APPRECIATIVE, ALL-KNOWING.﴾ [An-Nisa: 147]. The "what" is an interrogative of denial, meaning: He would accomplish nothing by your punishment. Allah does not benefit from punishment; rather, the disobedient harms himself, just as the obedient's action is for himself. Despite His mercy, Glorified be He, He is Wise and All-Knowing. He is not pleased with disobedience, nor with being disbelieved in, nor with His prophets being denied, nor with His servants being wronged. Therefore, He has promised a severe and painful torment to those who disbelieve in Him and wrong His servants, and this is from His perfect justice and power. The one who loves to torment people is he who torments his servants even if they are obedient, and he who does not grant respite, nor excuse, nor give his servant an opportunity to repent, and he whose primary characteristic is torment and whose instances of mercy are few. Exalted is Allah far above that.