To say that God is omniscient is to say that God knows everything. I would have to know everything myself to know whether someone else is omniscient. When I think about it, I would not want to know EVERYTHING. There are a few things that are not my business. Some things are my business such as my internal organs, but I would still not want to look at them and so I am glad they are inside my body. People seem to have an interest in knowing the personal lives of celebrities. I do not personally care which famous person just got married, divorced, or pregnant. I am sure that these things would be relevant to those people who are involved with them directly but I do not watch TV and so I never hear about someone until someone on Facebook is gossiping about them. I find the idea of omniscience to be irratiotnal and irrelevant.
Part of the reason I find omniscience irrational is because it assumes that God knows the future. If the future can be known, then it is already written and cannot be changed. This violates free will because a free will implies that humans have a choice in determining their future.
Some try to answer this by saying that that God knows what the choices will be. How can this be unless humans were robots that will do a certain thing at a certain time. If this is true then it is not a choice.
If we take the premise that God knew the future of what the world would become but that he still chose to create it. It means that he knew that millions of people would be murdered and raped. He saw ahead and knew about every death by war, abortion, suicide, and disease.
He knew all that and then thought: “Hey, that looks alright, I’ll start the world and let it become an awesome torture chamber.”
I think that explains why I have a hard time understanding why people try to defend this belief.