The Christians don't do those things because the Bible doesn't "call on them" to do it. The Old Testament is about how things were before Christ's sacrifice. It never calls on Christians to stone anybody, and that's why we don't do it. It's not just a subjective "I don't like this part so I don't follow it" mentality that Christians have. If that was the case, then even the blindest of Christians could see how much of a joke Christianity was. Fortunately, though, that's not how it is.