Apostate prophet remains cool; why hellfire threats in Quran?

In answer to the video "Walking Away From Islam"

With the issue of Hell and threats, the Quran employs rethorical devices conveying the idea of how no imagination can fathom this reality. The Quran only uses hints, through loan images derived from our wordly experiences, so that we may form an approximate picture of it. These hints are meant at making hell a threat and warning

101:10,104:5,37:62-65,39:16,17:60"a trial for men..and We cause them to fear, but it only adds to their great inordinacy"  

74:35-7"Surely it (hell) is one of the gravest (misfortunes), A warning to mortals, To him among you who wishes to go forward or remain behind".  

54:4"And there has certainly come to them information that in which there is deterrence".

Many aspects describing hell are said to be a trial and warning. The threat of hellfire, its grafic description throughout the book is actually a mercy from God, akin to those educational programs where inmates are encouraged to speak about the awful places in which they dwell, in order to reform potential criminals or discourage people from making the choices that would lead them there.

 It is like a shock therapy meant at breaking stubbornnes and unreasonable denial. Once that is achieved and that the warning is heeded, most will consider honestly listening to the message and ponder upon it.

The Quran was meant for all of mankind and the fact is that the vast majority of humanity will only maintain a good conduct and abide by the rule in the presence of incentives and deterrents. That is how society works or else one would remove all deterrents and simply expect the people to be morally upright. But the Quran does address the fact that some, will seek goodness regardless of rewards and punishments, simply by virtue of their nature and to please their Creator, the doing of good in cases where man has received no benefit. A stage in which a man's nature is so inclined to good that he has not to make an effort for doing good; he does good to all people as an ordinary man does good to his own kindred, looking at the whole comunity as his kindred 

16:90"Surely Allah enjoins the doing of justice and the doing of good/ihsan (to others) and the giving to the kindred".

The deterring nature of hellfire as described in the Quran applies to the tree of Zaqqum, emerging from the bottom of hellfire, yielding a type of thorny produce as repulsive as demon heads, tasting like the liquid that results from the washing of the wounds, boiling the belly of those that eat it out of desperation, neither providing with nutrition nor satisfiying the hunger 37:62-66,44:43-45,56:52-3,69:36,88:6.

In contrast, the gardens of heaven shall have all kinds of thornless trees ceaselessly providing every fruit, in abundance, within easy reach 56:28.

2000 years ago if a person had foreknowledge of airplanes, he would describe them to the people through the closest possible references known to their senses such as "big metal bird etc.". The Quran therefore uses parables or allegories to describe things such as the nature of the soul or other subjects unknown to men's senses like the angels, the process of revelation, the pleasures of Paradise, the sufferings of Hell and so on.

All these concepts are beyond our knowledge and observation; words have not yet been invented for them and their true meaning, shape or form are known only to God until the day we come face to face with such concepts and experience them. Hence the frequent rethorical question as to mankind's present inability to clearly picture what is in store in Hell 74:27.

 It is also interesting to note that the physical state of the dwellers of Hell, the form in which they shall be made is itself an alegory

87:13"And he will neither die therein nor live".

How does one who is in a state between life and death, physically experience the pain and suffering of hell? How does that special type of fire of which no human has any experience, a

104:6"fire kindled by God"

and

104:7"rising above the hearts"

be the means by which punishement will be inflicted? Many factors of that otherwordly realm are left in purposeful ambiguity because beyond human imagination. Sometimes when it gives a partial glimpse of hell punishments, it follows up by a vague statement about there being other similar ordeals in that place 38:55-8.

 It is to be noted, physical pain isnt the sole corresponding chastisement of the dwellers of hell. Their sins did not only cause physical injury to their victims, but also emotional, spiritual, etc. Thus, while undergoing this harsh but necessary process of "spiritual cleansing", the dwellers of hell will be made to experience many different types and combinations of sufferings, all related to their worldy deeds and the effects they had on themselves and their environement, from humiliation 46:20 to spiritual frustration to distancing from God's mercy/laan to physical torture. In fact it says clearly that the primary reason for them begging to come out of hell isnt physical pain, but grief 22:22. In the end, they will be purged of their sins and then their ultimate fate is left to God. In 85:10 for example it speaks of the punishement in hell as seperate from the punishement by the fire. The flames and its related punishments are said to be meant for the worst of the disbelievers, again, showing that not all sins require the same types of "cleansing method" 92:14-15.