Why do people only believe some of the bible?

Honestly, I believe in God, but not the bible. I think God would be able to accept anyone for who they are. But that isn't my question. This is just an example, but why do people say no gays, but then sleep with more than one person? Why do people think that the bible is the only true scripture, but don't stone there disobeying children? Why do people believe in Heaven, but don't kill anyone of a different religion? All of those are in the bible, I have read many versions of the bible front to back. Some may say the bible was written in barbaric times, but then why follow the other scriptures? I'm pretty much open to all opinions, I want to hear what you think.