I'm opposed to selective abortion mainly because I have known some wonderful down syndrome adults.  See my post about my friend.

But, it can be caught early, allowing parents to become educated and join the appropriate support groups.  Most problems come from families who do not know how to get the proper education and how to handle their children.

As for the "mansoom" thing.  I'm not sure how it is in Islam, but in the Eastern Orthodox Church, these individuals are called Holy Fools.  They are sent by God to teach us compassion and patience.  Its a grave sin to harm a Holy Fool and they are guaranteed a place in Heaven for accepting an imperfect body on this earth.   I may no longer be Eastern Orthodox, but I still believe harming one of these people (even before birth) is a grave sin and we fail that test. 

I cannot imagine my childhood without Stevie.  Nor can I imagine going to the Volunteer Fire Department in my home town without his smiling face.  Sadly, they do not live as long as we do and I fear I won't have my dear friend much longer.  I hope to see him on my next trip home.  His mother passed and my family said he has not done so well since she's been gone.