Who decides who has objective moral law? Do Christians? Or the Muslims? Who decides that one religion has all the truth and everyone else must accept this?

Nearly all Christians, and even Christ himself believed in personal freedom, to a degree. My point wasn’t who has the objective moral law; rather, simply that an objective moral law does not exist if there is no God. Any concept of right our wrong, good or evil is utterly subjective.
I don’t need God to give me hope. Seeing people of all races, of all backgrounds, of every belief under the sun, find it in their hearts to be good, decent people - gives hope, happiness and meaning in my life.

Do you hope for a happy afterlife? This is the ultimate hope I’m talking about, not filling your life with many little meanings, under an overall arching meaninglessness.
Some people like to enslave little girls in the sex trade. If there is no God, this is also a valid expression of finding meaning. (And I know you would deplore this kind of act.)
The Nazis believed God was on their side. The SS put ‘God with Us’ on their belts and buckles. Hitler felt the hand of God in his destiny to bring about the 3rd Reich and exterminate the Jews. With God on their side, why should they care what the world thought of them? They didn’t. The Islamic fundamentalists feel the same - the whole world might hate them, but this doesn’t matter when God is on their side.

This was a perversion of what Christ taught. Just because someone claims to be something, doesn’t mean they necessarily are. Likewise, it would be foolish for me to say that Stalin represented all atheists.
Equally there are stories of people converting to Islam from a life of hopelessness. But doesn’t mean Islam would be right for me. In fact it would be a waste of time as i’m not convinced God is real.

No, not equally. Islam may have some stories, but the majority of their followers are born in their religion. Christianity is larger and has far more converts. Furthermore, Christianity has many miracles (signs, wonders, healings) whereas Islam does not have 1% of this kind of phenomena.
No. I would not bow down to a tyrant in whose name millions have been killed and countless millions have been enslaved. That would be like following Hitler or Stalin.
This is a nonsensical comparison.
If you think this was God’s will, you are mistaken. God never desires evil; when suffering happens it’s part of his permissive will, just as man has free will.

Keep in mind that for every evil “Christian” there are nearly a hundred Mother Theresa’s (or people like her) out there. How many atheists do you know that have this kind of dedication? They don’t exist.
God loves you, whether you care or not. He will keep chasing your heart until the day you die.

I believe that I should try to be a good person because society and my fellow human beings deserves nothing less. Whether God exists or not would not change this.
Somehow you still believe there is a good by which mankind should be governed. If God does not exist, this forum, thread, my post, your thoughts, and my thoughts are ultimately meaningless. You try to be a good person. How do you define good? Define it any way you want; there is not standard for good or evil.
The golden rule thus becomes fool’s gold. It’s like writing a book on how the world is essentially meaningless, all the while assuming your book is meaningful.
U r doing good, and u r happy. So why can’t u accept other people can be just as happy being something else other than Christian? As long as the person is decent and does not hurt other people, why should it matter that he should be of a particular faith?