Exactly what the title says, Christianity in all its various strains still stems from the horrendous old testament, and with all the awful shit that endorses, as well as with things like Calvinism and the general doomsday cult foundations in the religion, why do some people still act so charitably towards it? Christianity has proven itself to be a morally corrupt and oppressive institution at every turn. Or maybe I'm just too negative? 
EDIT Ok guys I get it this was rather reductionist, and I definitely was disregarding all the good that religious folks have done, and that religion has inspired people to do, but again over correcting into enthusiastic support for religion can also be problematic.
This is gonna blow your mind, but you can be religious and a good socialist at the same time.
The church closest to my home is where I do some of my community gardening. They know full well that I'm a socialist, an atheist, and bisexual, and they don't care in the slightest. As far as they're concerned, actions trump beliefs—good works are God's work, they've told me. They're fundraising to build an affordable housing co-op for displaced First Nations folks in the community, and they broke ground on the first block last year!
Theory didn't stop in 1844 when Marx said we need to move beyond religion for the working class. We can do better.
We can move beyond their garbage beliefs. The Bible is trash and should be treated as such. It promotes hate,removed, murder, genocide. Oh such good values to uphold.