OP, you just demonstrated that you don't understand the very basic belief of Christianity. Were you not raised in the US?
Christianity is about Jesus Christ. Jesus died on the cross as sacrificial payment to God the Father. It is the only suitable payment to absolved us from death, as the penalty for sin is assuredly death by God's law. Why do you think Christians call him (JC) the savior? Why do you think Christians believe that non-believers are condemned to hell (death)? The point is everyone sin and deserve death but only Christians (who are also sinners) are saved.
I was born and raised in the US my entire life (full disclosure - in a non-religious family and I never went to church). I had heard a few vague things about how God killed lots of people in some parts of the Bible. I did not really understand how the more ruthless passages of the Old Testament were reconciled with the more loving, understanding New Testament until maybe a couple years ago. I didn't really look into it, but it's not something I was ever taught or ever encountered on my own.
You simply can have no meaningful grasp of history of Western Culture without it. Do they teach nothing in school anymore? Are you incapable of drawing those conclusions on your own? Do you understand anything about US History even, much less Europe? Christianity is central to all of that. Christianity, like it or not, is the dominant force that shaped all of Western culture for the past 2000 years. Your ability to speak and act freely is due to Christianity. Your ability to openly challenge Christianity is due to Christianity.
The odds of you coming here and making this thread in ignorant and blissful innocence are 1 in 983298632986. That's how about how many threads of this nature I have seen on this board alone, and they are all troll threads. That's because people use those passages from the Bible to smear Christians and Jews, ala "Look at how a bunch of fairy-tale believing retards want to run the world. Even if they don't how can they call that book sacred? Only a bunch of backassward monkeys would buy any of that garbage!""
Now if you seriously have questions about this topic, you are putting the cart before the horse. You need a history of religion class or two, or five.
Did you not study this book in school? Do they not teach the Bible in public school anymore?
OP's question touched a nerve and I can see why... those particular books of the OT are used so much by militant atheists as a smear against Christianity. And it's true, in most cases, when someone cites a Leviticus passage saying you are supposed to stone people for this or that, it's trolling. But this is FBB we're talking about and I think there are actually a fair number of people who legitimately don't understand why there are such things in the Bible. The whole "Jesus died as a way of taking care of all that nasty OT stuff" explanation isn't exactly obvious to non-Christians. All I've ever heard was the line "Jesus died for our sins," and I really didn't know what that meant either.
I've seen how some atheists can be real jackholes about these things, and I've made it a goal of mine to not be a jerk about it. I am constantly putting forth an effort not to judge people based on their religion. But I still sometimes judge the religion itself. And passages like the ones OP posted make it hard not to.
But yeah, to answer your other question, no, they didn't teach us very much about religion when I was in school. The historical aspects of it, sure, but not scripture. It has no place in schools anyway; if you want your kid to learn scripture, send him to Sunday School.