Since we model that being as having similar motivations, desires, etc., we believe that God will also follow some sort of morality and subscribe to basic ideas of fairness.
Also, consider that we exist. If there is such a supreme being, then logically, that supreme being does not object to our existence (since we have not yet been smited). Therefore, to said supreme being, our presence is either desirable or irrelevant. If desirable, our presence can be expected to continue; and the human ego will not allow many people to seriously consider ourselves irrelevant, so that option is often simply not considered.
Also, consider that we exist. If there is such a supreme being, then logically, that supreme being does not object to our existence (since we have not yet been smited). Therefore, to said supreme being, our presence is either desirable or irrelevant. If desirable, our presence can be expected to continue; and the human ego will not allow many people to seriously consider ourselves irrelevant, so that option is often simply not considered.