Is the muslim god fair?

[Muslim Scholar]

People are not equal
It is justice, which means that God applies the same rules over all people

nope he doesnt.

A kid between a muslim and a non muslim has to be given to a muslim, non muslims have to pay taxes, and non muslims are generaly suppressed.

You don't understand the meaning of justice
The same rules applies, but as the rules include parameters like being a Muslim or not then it apply differently
Same like giving a fine for speed driving, they don't fine people who are driving below speed limits.

You fail to understand the concept that a justice system may treat criminals different from inocents - yet in order to be just - has to treat every participant of sociaty equal and give them the same rights.

Exactly
A non-Muslim is a criminal in the Islamic view