Yes, Christians realize that. Do you realize that Christians were largely responsible for ending slavery worldwide? Yes, it was Christians like William Wilberforce that helped end slavery.
The world is filled with injustices and suffering and Christians did not end all of them. Christians are a part of the social network and changes take time. However Christians are also responsible for instituting public education for the lower classes. Christians opened the first general hospitals, the first orphanages, and pushed for social justice for the marginalized.
When social norms believed in witches causing horrible things to happen, they targeted witches. Christians zeal to correct social problems have sometimes caused them to go awry. This is also true for the Crusades and the Spanish Inquisition. Yes, it would be nice if Christians never made any mistakes, but Christians are also humans, and often driven by perceptions common in society.