1. Utopia
The nature of Heaven is generally agreed upon: it is a utopia. A perfect place in which there is no sadness, fear, anger, pain, or sin. A place full of love and togetherness, where everybody gets along and there is no hatred. In Heaven, everybody loves and praises God most of all, not because they are forced to but because they want to. There is still free will, but nobody chooses to do otherwise.
As long as that can be agreed on, the following arguments can be made.
2. Nonexistence
The first argument is simple: Heaven, by its own rules, cannot exist and remain perfect. This is best illustrated by examples.
Example 1: While alive, I fall madly in love. Then, there is a terrible accident and both I and my significant other die. I, being a devout Christian (note: this is not true, I'm simply using it as an example because it is generally the Christian belief that only those who follow Christ will get into heaven and I am using it for the sake of argument), go directly to Heaven. My lover, however, though a good person, is not Christian, and therefore is sent to Hell. How am I to be happy in Heaven knowing my lover is being subjected to eternal torture? Remember: there is no sadness in Heaven.
Example 2: I die and go to Heaven. There is no fear in Heaven, yet I am still expected to fear and revere God ("Fear God and keep his commandments, for that is the whole duty of man." Ecclesiastes 12:13 NIV*). How is this possible?
There are other examples for anger, pain, and sin, which will be posted on request.
Now, if a soul is not completely happy but is in Heaven anyway, Heaven is not perfect. If there is no fear in Heaven yet one is still expected to fear God, Heaven is not perfect. If Heaven is not perfect, Heaven is not Heaven and therefore it disproves itself.
3. Emptiness
This argument is linked to the nonexistence argument; it states that if Heaven does exist it must be empty. The only logical way to prevent Heaven from disproving itself would be if it never had an opportunity to. If nobody ever went to Heaven, Heaven could still exist because it would remain a place with no sadness, fear, anger, etc. Once a soul is sent to Heaven, however, the nonexistence argument goes into effect and Heaven ceases to exist.
The opposite of this could also work – if everybody got into heaven, everybody could still potentially be happy. If that was the case, however, Heaven would not be very different from Earth and it would be far from perfect. Which leads into argument #4…
4. Dystopia
Before reading this, it is important to have an understanding of what a dystopia is. A dystopia is the antithesis of a utopia; it is designed to be a perfect society but is instead the exact opposite. In dystopias, the general population does not realize that their lives are not perfect. They believe that everything is the way it ought to be and that they are completely happy. They respect and love the few in charge of society, and they accept everything they are told and given without questioning it. There are a few people, however, who realize that all is not right and society is actually corrupt instead of perfect. These people are suppressed or destroyed before they can cause too many problems from those in charge of society.
What does this have to do with Heaven? Heaven, like every dystopia, is meant to be a utopia. Everyone believes that in Heaven souls are completely happy, and that everything is perfect. Everyone in Heaven loves and respects God, the being in charge, and everyone accepts his word and his gifts. The few people who defied authority, Lucifer and the other fallen angels, were exiled. Heaven is the ideal society.
However, an ideal society is simply not possible. The only way to make sure that all of the people are happy all of the time is to completely remove the capacity for free will, either by removing free will itself or removing any options other than one. If there is no sadness, fear, anger, pain, or sin in Heaven, a soul has no other choice but happiness and goodness. There would be no free will in Heaven because of this, and without free will the soul loses everything that defines it. There are no choices to be made, because they are all already chosen; there are no individual actions to be made, because everybody must do the same thing because there are no other options. People are no longer people, but empty shells, not only unwilling but also unable to rebel against authority (due to the fact that they believe they are happy and the fact that they do not have the capacity for anger, individualism, etc.), a situation typical of a dystopia.
*For further quotes from scripture supporting the fear of God, go to http://www.feargod.com/why_fear_god.htm.