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.
Judaism also stems from the old testament, should we remove Jews for what is in their holy book?
The Catholic Church (And the Anglican Church, and many Lutheran Churches, and thousands of Baptist Churches) has committed great evils, but original sin is not a marxist doctrine and we cannot hold the average Christian responsible for the actions of everyone everywhere who professed the faith, and you are not likely to see support for such things amongst the Christians posting here. If a Christian is supporting the slave trade or the nazis on hexbear they are likely to be banned and find no support among other believers.