Agree with Ron's analysis!
Once we accept thresholds upon which life becomes expendable, we create a slippery slope toward eventually determining that any life is expendable. Who are we to decide what percentage or number of defects is too much to make life worth living? I suspect that much of this talk is really selfishness in that X does not want to care for a child with defects so, "out of concern and compassion" X ends the child's life "lest it suffers too much." So much drivel wrapped in fertilizer!