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.
Christianity as an organization of political power is a horrible stain on humanity and likely always will be.
Christianity as a personal or small community religion is actually a really beautiful and hopeful thing. Christianity does not start and end with the old testament, it ends with an overcoming of many of the regressive messages within the old testament and strong recurring themes of hope based around community. The bible is a pretty important world text and has a lot of great messages in it.
Basically, attack systemic issues and organizations rather than individual beliefs.