Imagine a judge who punishes every suicide identically, ignoring mental state. That would be unjust. But that is not the God the debate assumes. I think the question smuggles in a premise: that God sends everyone who dies by suicide to hell. That premise is not established, and mainstream theology does not teach it. A just God weighs knowledge, freedom, and culpability. Severe depression or psychosis can crush free choice, and a fair judge accounts for that. Hell, in the tradition, is about persistent, unrepentant rejection of God, not one tragic act. So the charge of moral injustice falls apart. You cannot call a judgment unjust if you have misdescribed it. The stronger position is that God's justice is not ours to measure by a single act.