This. By weaving their politics directly into religion, they get to benefit from the inherent suspension of disbelief that religion requires. No amount of proof or evidence will sway a conservative because the blind faith that all proof and evidence is fake is the key point of conservatism.
I understand where you're coming from, but it's not an either-or situation. Many conservatives hide behind religion to do heinous things. But there are plenty of religious people who don't fall into this "conservative" definition and do heinous things as well.