Excellent question. We have granted ourselves permission to eliminate the weakest, most dependent among us. I say "permission" because we have no "right" to take the lives of pre or post-birthed ********, the infirm, brain-damaged, aged, etc. We have accepted and baptized murder as a morally defensible act when, in fact, there is nothing about it that is defensible or moral. What it is, IMO, is simply justification to not be inconvenienced by anyone or anything that does not provide for our immediate gratification and ease ... selfishness at the cost of another's life.
Ah, but I go on ....