Theology (unlike Biology, for example) is not the study of God, but what one already believes and teaches about God. Theology, in this sense, represents not your pursuit of God, but what you think you've already grasped about him. Theology has been subtly replaced by dogma, and dogma is enforced by the validity of the institution, and vice versa, the institution is validated by its dogma.
Therefore, if others who are studying God (theology, in the biology-like sense) find something other than that which our institution already holds to be true (theology, in the dogma sense), then those findings threaten the validity of our institution by challenging our enforcement of some particular dogma.
Coexisting means we have to be humble enough to accept that there is a range of uncertainty about God, a range our dogma does not allow. So, we find that we must choose between coexistence and our institution. For us, the choice is obvious. We must side with the institution and defend its power, or the "truth" will be lost to the pagans!
Thus, peaceful co-existence is bad for our power struggle, and therefore bad for us.
It does not phase us that the central story of our faith revolves around an episode in which a man challenged the predominant religious institution of his day to set down their struggle for power in order to co-exist with those they saw as enemies, and to love freely. In our story, they killed him over this, and we praise him for that martyrdom, among other things. We make villains out of that institution and its struggle for power. We think we're better than they were. We think we understand God better than they did. We think we grasp that man's message as they clearly did not.
And then, we show we are just like them by spouting off rhetoric that is not fundamentally different than theirs. We choose power over love, judgment over co-existence, fundamentalism over humanitarianism. We choose sides by creating sides. We choose to preserve the church over preserving the truth.
At least, that's what it looks like from the perspective of most non-Christians I minister with, which is the number one reason they are content remaining agnostic. Maybe we can afford some unaffiliated peer review. Maybe.