One of the objections people give to the concept of Hell in Islam is that the crime of disbelief is finite while the punishment is infinite. They say this is unfair. For the sake of this article, I will assume the reader already knows that beliefs can be punishable. See: Can false beliefs be immoral or deserve punishment?
The crime that is punished with infinite punishment in Islam is when someone disbelieves after having known the message of Islam and dies in the state of disbelief. Any other crime can be forgiven and will not be punished infinitely.
First, one needs to dismantle the notion that the time or length of a crime must be proportional to its punishment. Let us take the example of murder. A murder takes less than a few seconds, yet most people agree its punishment can be up to a whole lifetime.
With the same logic as this question, the murderer’s lawyer can ask: How can a few seconds of bad choices lead to an entire lifetime of punishment?
We know murder is punished so much because the crime itself is evil enough to deserve that regardless of how long it took to commit the crime.
Second, one needs to understand that the severity of crimes commonly depends on whom it is done against. Everyone agrees that a person who murdered a stranger is not as evil as a person who murdered his own loving mother that never did any wrong to him.
Even though the crime was the same in essence (killing someone unjustly), the second was more evil because of whom it was done against.
When you owe someone something or when someone deserves honor and respect, committing a crime against them is even worse than normal. The greater the person and the more you owe them, the more evil the crime is considered.
Third, one needs to look into himself and unpack the biases he has. People are affected heavily by their culture and society when trying to understand the evilness of a crime.
A person who has grown up in a secular society or has absorbed secular ideals will unconsciously reduce the importance of God and the severity of crimes against Him.
On the other hand, someone who has absorbed belief in God will automatically increase the severity of crimes against God.
So, a person should know that his biases play a large role in what he considers severe. That is why the objection is largely meaningless. It only seems like the punishment is undeserved because the person doesn’t place much severity in crimes against God.
The person should also know that God is the most perfect of creators and most loving of caretakers. When a crime is committed against someone infinitely perfect, it fits the crime to punish it with infinite pain.
Finally, he should realize there is no basis in the objection from length of the crime. The crime can be punished infinitely if it deserves infinite punishment and that has nothing to do with how long the crime was done.