“There has to be some rational mercy to make capitalism work.”
No, there doesn’t. Capitalism is self-correcting, with or without mercy.
Christianity is the reason why socialism cannot die in the West; it gives the people the false impression that self-abnegation, particularly self-sacrifice, is noble in itself.
I think you mean "the misuse of Christianity"
Otherwise that would mean you don't know what the words Christianity or Socialism actually mean.