if we got rid of all of the birth defects, we'd stagnate, we'd stop evolving. you don't want that.
if you want to be an autism advocate, there's two ways to do this:
1) the most humane choice in many cases is abortion.
2) in cases where the autistic child is not so retarded as to be able to live a life, they need lifelong support, and state resources to provide it to them.
it may be possible in the near future to determine if a gestating child is autistic via a dna test. it would not be conclusive today, but you could catch a lot of it. that research should be funded.