So do I. But believing in the Bible and recognizing the actual history of what has gone on/goes on in the world are not mutually exclusive. Does the Bible set down certain standards by which Christians should behave in order to best live their faith and bring other people to it? Absolutely. But the key word in that is 'should'.
Even the Holy scriptures themselves recognize this, as in the candid words of our father St. Paul in his epistle to the Romans, wherein he shares his own struggles to live according to the 'inward man':
7:21 I find then a law, that evil is present with me, the one who wills to do good. 22 For I delight in the law of God according to the inward man. 23 But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members. 24 O wretched man that I am! Who will deliver me from this body of death? 25 I thank God—through Jesus Christ our Lord!
Is this not also part of our lives in Christianity -- that we do not always do as we should? It doesn't excuse it, of course, but it does show that if even our fathers the holy apostles also struggled to live rightly, then things cannot be as simple as taking individual verses to use as shields against criticism for doing things that we really shouldn't be doing anyway. "Who will deliver me from this body of death?" is self-reproach, and hence certainly not as easy to read as verses that tell you how to spot a liar, but it neither contradicts those verses, nor allows the believer to substitute one for the other such that if you know you don't fit the description of one verse, then you can be sure you do not fit that of another that is more inwardly focused. "These you should have done without leaving the others undone", remember?
We harm ourselves and our ability to progress and have healthy spiritual lives by selectively focusing on those things that make us feel better, or that we do not personally have problems with. Again, it's good that you have a verse that you say allows you to distinguish a true Christian from an untrue one, but that does nothing to address the problems created by the behavior that Voices That Carry mentioned, which are deep, long-lasting, and largely unresolved precisely because it's not possible to have an honest conversation about them if every reply is essentially a salve to make Christians feel better about the reality that some of their coreligionists killed people, subjugated people, etc. And I know that the Holy Bible encourages honest talk and sincere inquiry. ("Let your yes be yes and your no be no", "Come, let us reason together", etc.)
Lord have mercy.