This line of thinking is used as a “gotcha” for Arminian believers. Like “Gotcha! You’re saying Hitler is going to heaven and that is indefensible!” My response to it is:
If Hitler were alive today and you met him, would you present the gospel to him or withhold it so that he can be punished eternally to your liking? The entire point of Christ’s death was to give us a way to avoid the punishment that we earned, Hitler included, because God is not willing that any would perish. So, if you’re looking for justice and consider eternal torment an appropriate means for those ends, then according to your theology, you must deny Christ now to ensure your own seat in hell because that is the only way for justice to be served. Your denial of Jesus would ensure that you receive the justice that you demand for others.
Of course, the obvious truth is that you consider your own sins to be relatively insignificant and minor, only needing to be whisked away by a little sprinkling of Jesus’ blood, whereas Hitler would need more of Jesus’ atoning blood than is available.
This argument of “justice” is simply selfish. I am not downplaying the atrocities of these mass murderers. They were obviously unjustifiably wicked. But they didn’t do anything that you are not capable of and might do if you were in their shoes. I’m not saying you would, but you might. Remember, we are granted our personalities, tendencies, bodies, health, demeanor, etc. The right combination of these things could produce evil in any of us. And given the right circumstances, mixed with the other variables of our personalities, might lead us to do the same. Maybe not… but maybe so.
Either way, we should not claim “justice” as proof that God is going to torment people for eternity. If that is our measure, then it will be measured back to us. If it is justice you want, then it is justice you will receive. Are you sure that’s what you want?