We do have some violent instincts. We have conciliatory and cooperative instincts too. If we're conscious enough, we can choose which ones to follow. If there is such a thing as human nature, then the ability to decide our own actions is also a part of it.
As for the benefits of religion, I believe they vary from one person to another. Everyone has reasons for what they believe in (some of those reasons are conscious, some others aren't). I don't think it matters much what anyone else's reasons are, as long as they don't try to force their views on other people, nor attack others for their beliefs.