Remember: It was Cain (a murderer) who replied to God, when asked where Abel was, "Am I my brother's keeper?"
There are hundreds of verses and passages throughout the Bible (and other religious texts) that say, quite explicitly, that we are our brothers' and sisters' keepers in some way and to some extent.
It is the determination of the way and the extent where there can be reasonable discussion and disagreement. (For Mormons, however, King Benjamin's sermon sets an incredibly high bar for refusal.) For Christians to deny their responsibility to help "keep" God's children (any of them), at all or minimally, however, is a direct denial of the ministry and teachings of Jesus, of Nazareth.
Quoting Cain in doing so is the height of irony.