Emotional response: I am completely against aborting any child based on genetic screening. My friends have a son with downs, and they made the choice to continue with the pregnancy despite their fears and knowing that he was very likely to be born with the condition. They have never regretted their decision to keep their child, and after birth he has surpassed all medical expectations in terms of growth and neurological development. I am very happily the god-parent of this child, and will become his care-giver if anything happened to his parents.
Scientific response: If you believe in evolution through genetic mutation, then aborting based on mutations is a bad idea. Reduced genetic diversity is usually considered a bad thing for the overall survivability of a species. What we consider to be a 'bad' mutation may be the mutation that saves humanity from an unexpected environmental change in the future.