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.
I think religion is good.
Sorry I guess, but i've run the gamut in my life. I used to be a little edgelord preteen that delighted in shitting on belief. i had an earnest christian phase. i had a heresy and occult phase. i'm still in an "academic study of these matters is cool as hell" phase - I think if you're overly reductive, you get it in your head to only measure what religion does on a socio-political level, and this is a fucking trap. Anything tied to power structures can and will be abused, but that doesn't make these places the sole determiner of worth and value for anything, but for religion it's especially busted.
Religion and spirituality are like, really important elements of the human psyche. I can't tell you why that is, but I can tell you that even in instances of non-belief in an individual, the overwhelming tendency is that other structures replace it and act as a surrogate - something in our mind needs whatever religion provides. It can get it elsewhere of course, i can think of some large social projects that tried to redirect that impulse towards common, human-centered goals and sometimes, for some people, it works, but it's at least clear to me that being reductive about this and treating it as problematic or bad or somehow more trouble than it's worth, is coming from a place of disinterest and lack of understanding.
Religion is the opiate of the masses. Perhaps in a less sick and damaged world their would be no need for such a medication to ease their suffering. Maybe we'd already be living in that world if they'd stop waiting for the afterlife and actually care about the world around them for once.