The most important reason anyone is an atheist

[Sword of Christ]

Then why do conservative Christians always find themselves on the wrong side of those human rights movements and welfare systems?

You can appreciate there is a right side rather than the right side being whatever your own opinion happens to be. See how you understand Gods Moral Law? But yes some Christians are douche bags, some atheists are douche bags, some Hindus are douche bags and you can go on. Though we're all douche bags to some extent, that's the sin at work.

I'll give you a few examples: Women's suffrage, civil rights, gay marriage equality, and Republicans always trying (and occasionally succeeding) at cutting social programs, like for instance the recent $40 billion cuts to SNAP?

I'm sure they would do the exact same thing if they were all atheists.