Why not? You expect as much in your everyday life. You would certainly take issue with a friend or relative who claimed they had an invisible friend who could magically make things happen. If not in the interest of objective truth, at least in the interest of that person's sanity. Besides, theists are notorious for thinking ill of those who don't believe in their god. Whole levels of hell have been imaginatively contrived to accomodate such heretics. Don't you take issue with that kind of thinking?
Not all theists are interested in "converting" others to their way of thinking. That said, I'm not interested in changing theists' minds to my way of thinking. I was once a religious person and it has been a long and winding road that I've traveled, to get to where I feel content as to my beliefs. As content as I can be, for the time being.
People have to find their own way as it relates to spirituality, etc...
Don't get me wrong, I understand the premise of your thread. But, I'd hate to see atheism/agnosticism morph into a "religion" unto itself ...the very thing it's speaking against. That is more of my point.