It comes down to the fact that conservatives (in general) recognize the principles of objective morality, objective rules, and objective right and wrong.
The left, in rejecting God, also reject objective morality, rules, and right and wrong.
The only way to determine what actually IS right is POWER.
Who controls the power of the state controls “god”, so to speak, because they control the power to set morality, rules, and what is right and wrong.
This is why they are so attracted to State power and therefore to politics.
This certainly is what compells the gay lobby, I don't know why it wouldn't apply to the rest of the left as well.