>   whatever happens to a person is written by Allah in his fate (Again, please correct me if I am wrong.)
>
If that is so, that means the murder of the person was already written by Allah in his fate and had Allah's acceptance.  Then why it is considered major sin?


DONT BELIVE FATE, why? because by believing fate you will ignore heaven and hell.
FOR EXAMPLE,when you playing chess you will anticipate your opponent next move and you will do something about it.
ALLAH knows what we will gonna do Allah shows the true path to us but those who dont listen to Allah, will go from wrong path and they will commit sins.

and thats all.

Fate is something we build it. we can think and decide for ourself.
and thats prove it.