The 'old testament' argument

[iameatingjam]

This is a question for theists. I often come to a point in discussion with religious people where I start pointing out horrendous bible versus. They usually say something along the line of 'oh but that was in the old testament so it doesn't matter'. What?? Its the word of GOD but it is irrelevant? So god came back and changed his mind?? He created the universe but as soon as social norms change so do his? What is the rationale behind this? Thanks.