most believers avoid doing evil because of fear hell
So what would happen to people if you took the fear of Hell away?
human will commit more crime without guilt
That is quite simply false as I and most of the people here who don't believe in Hell can attest to.
But lets assume that it does work - at least on some people.
There is no reason to actually carry out the punishment in the next life is there?
These 'criminals'

(people who don't believe) are not going to commit any crimes now are they?
They have died and left this world.
There is
no reason and no need for God to keep someone alive for ever just to torture them over and over again.
That is just sick and sadistic?
Or are you saying that Hell is just an empty threat meant to scare people and God won't really burn anyone?
Which is it?
you and i understand islam differently
many thing in the quran i dont understand but enough for me to believe in