(1) Temporary acts don't merit forever recompense.
When it comes to paradise, no one has a problem with it because it's an act of forever gratitude from God. It seems the problem with hell, is because it's a forever wrath and vengeance from him.
The issue seems to be then not about temporary vs forever, but an issue if forever wrath is the proper response. If forever gratitude and reward for goodness is the proper response, seems rational, forever vengeance and punishment is proper response for evil.
(2) God loves us more then we love our children.
The Quran shows that family were cut off by companions of Mohammad (s) and even fought some of their own family, when it came to truth. That is not that they didn't have affection and care for their parents, or siblings, but they detached themselves at the moment of battle between them and when their opponents showed hostility and fought the Prophet (s).
Of course, they direly wanted them to be guided, but at the end, it's not in their control.
The issue is God does want to save us before we die, and tries to intervene through intercession of his chosen from humans and Angels, and try to guide us, but at the end there is consequences for having died evil.
(3) Why can't we just change on judgment day?
This is a question. Why can't we change after? The reality is, good will and motivation is not possible in this scenario. It becomes purely a selfish act and the prayer is purely selfish with no love of God in it if you ask for God to forgive you at this point.
God set it up that death is like a pressure that motivates good deeds. That is we wish to help ourselves and others in terms of peace and guidance and relationship to God and his chosen lights on the mystic journey.
The choice is that there is forever consequences in preferring that which is lower (darkness) over that which is higher (light) and to journey downwards and running away from God's light, there is consequences.
Of course, if there was no consequences and we had forever time, it makes this trial of life with all it's complexities and simplicities meaningless.
For life to be a lesson with no consequence or reward, would make the nature of good and evil a joke play by God, it bears no reality.
On the other hand, that we have to face consequences of our actions and the faith gains light from good actions and good actions repel and purify evil actions to bring one closer to faith if have no faith, is the trial.
This also shows for similar reasons, hell is forever, as nothing can calm down God when you can't do anything of merit anymore at this point.
(4) Three things caused them to go to hell per Quran and if one was done, they would have avoided it.
(1) didn't connect to God through his established way of connecting'
(2) didn't emphasized on feeding the poor humans in need of food (Yemen ahem Yemen, etc)
(3) would vain talk with the vain talkers
If any of these are avoided or positively done (negated), if one connects to God, the other two will be avoid. If one seeks to take side of oppressed and feed the hungry, they will want also the world solution for this, and would see that lies in accepting God's guidance and kings appointed by him for justice. If one avoids vain talk, they will realize the seriousness of the two above.
Any of these, caring to feed poor, or connecting God through proper avenues, or avoiding wasting time in vain speech over and over again in one life time, they would've attained salvation.
But when all three of these are avoided...
(5) Justice is a reality
Everything no matter how little or big is assessed. None escapes God's judgment, guilt is a warning sign of a justice taking full form one day with respect to evil deeds.