how is disbelief arrogance?

It becomes arrogance when a person is not willing to reconsider!
As opinionated as I am, I still have to stop and reconsider my position before I answer a question. I re-examine the validity of what I do believe.
But I have been blessed with some hardships that I have endured that have strengthened my faith and understanding. Others have not and in all reality answer in a prejudice way, this includes those on both sides of some disagreements.
In all honesty, I don't believe atheists, agnostics and most theists have enough experience to give an opinion of some issues. Some have not realized that the truth in many cases is between the two extremes. There are some issues that only death can resolve for the person to have 100% certainty of knowing. On that one, the answer has been given to me by a limited experience with death. There is a soul and of that I am positive! If there is a soul, there is a God.
It is just one of those things that by the time most have the proof they need, it is often too late to change ones mind on the issue. I feel for those who have no contact with that inner part of themselves that continues on once the body ceases to function. They are going through life as half the person they could be and that is their loss.