I'm specifically thinking about the divinely commanded genocides, though I'm sure I could come up with other complaints if pressed. But if one of the key commandments of Christianity is to love your neighbor as yourself, even your enemies, how can genocide ever be justified? I don't see any way to reconcile these things that does not put morality completely out of the reach of human understanding and therefore as good as nonexistent. I would not say "Stalinist theism," but it does have more than a touch of Islamic authoritarianism to it, in that moral truths can be known only by revelation.
Yes, I got the reference to "divinely commanded genocide(s)." That particular issue seems to be one of the main deal-breakers for a whole lot of people. And I have some theories as to why:
1) We in the Post-Holocaust West are stuck in a social paradigm shift in which we are tempted to completely discount the value and graveness of "sin." That concept just doesn't register for us. "Crime" does; "sin" does not. Some of this shift began in the Renaissance, but really got going after the European religious wars finished in the 1700s, with the 20th century Holocaust and Communist pogroms and tyranny providing yet additional catalysts for this shift. See law professor Gordon A. Christenson's (2012) article about how Enlightenment, Modernist thinking has brought about a legal sea-change (social paradigm shift) for the practice [and understanding] of religion in the West.
[Please note: I'm NOT saying or implying that peace is bad. Obviously, "peace" is a cardinal idea of the Christian faith. The caveat is that the Christian faith implies that real social and political peace can only be found in Christ, and can only be had if everyone gets on the same religious page ...]
2) Many people today think the Bible, or New Testament specifically, extols a generic concept of "love" above all else, but it really doesn't. If anything, it emphasizes God's "love" in Christ for the world, but it does so conditionally and only in tandem with
all of the other aspects that are central to God's View Point. What this shows is that not many people are given to reading the Bible very closely, or correctly, and they have no desire to even contemplate hermeneutical applications in their reading. They think everything should be simply interpreted, that God would have made it simple, and thus our conclusions should be intuitively simple. However, if the God of the Bible is truly real and in accordance with a full and complete reading of the Bible, I think we can see how this reaction among people can be seen as the onset of a gullibility that comes with the paradigm shift I mentioned above.
3) We have people today (many Christian, even) who promulgate either superficial understandings of the Bible, or at times, erroneous ones which lead others into confusion, making the undertaking of serious study of the Bible not so much a difficult one, even though it is, but one prone to the emotional detachment and complete emotional aversion (and now avoidance) that comes with the apparent lack of relevance the Bible has for people now living in the same paradigm shift.
Those are my initial theories. Of course, as I've said before, there's more where that came from ...
As far as Islamic authoritarianism is concerned, I'm not sure how that counts against the truth value of the Old Testament. To me, attributing fault to the O.T. by referring to a later contrivance such as Islam is anachronistic. Besides, Islam is discounted straight off the bat by Christians because the weight of the disagreement they have with Muslims is much, much heavier than the weight of any theological agreement they may also have. That is, since Islam denies that Jesus is the Son of God, and denies that He died on the cross and rose again, denies that humanity is reconciled to God by the person and work of Jesus Christ alone, this one most important point itself proves the inefficacy of the late-comer to World Religion. So, it should immediately be swept off of the table of discussion for any further consideration from a Christian point of view and not count against Christianity, or against the remaining, post-resurrection cogency of the O.T.