The Muslims certainly do not reject Allah because of Jahannam (the Koran’s “Hell”).
You’re missing my point.
God permitting hell is a moral scandal to some people. To them, if that God existed he would be an evil God. People stand up to worldly dictators sometimes and are tortured and killed for it but most lay low and appease them. Suppose the dictator were eternal and all-powerful - that still wouldn’t make him good, would it? You could not gain anything by opposing him, not even non-existence.