Christians claim that morality must be absolute, hence a need for God.
But that is just morality from authority. And it is a poor basis for morality. It assumes the authority is good and perfect, but that may not be the case.
I would argue that morality is in actual fact always subject, not objective. Even the Bible says so! God says "though shall not kill" but then orders killing by divine decree. IN fact it is his go to solution for most things. So it is claiming that murder is subjective and the authority gets to decide when it is a sin and when it isn't.
There are many secular ways of forming a moral construct (or foundation if you like) that don't require a God or an authority that I think a better than morality by authority, and even these will shift over time as we continue to understand the world and ourselves better.