if you are told the baby you are carrying has a chromosonal abnormality (downs syndrome being just one, perhaps the most well known) then the problem is that no one can tell you the degree to which your child will be affected. there are many health complications that go hand in hand with downs - including heart, lung and digestive problems.
we have friends who chose to go ahead with their pg knowing their baby had downs, and miscarried at 38 weeks. They had been told that about 80% of DS babies are MC/stillborn. They had hoped they would be in the 20%.
So,the DS adults we see living in the community, working, being able to have a relatively happy, healthy, fulfilling life are the very thin end of the wedge. we dont see the ones who died very young, who suffered very painful operations from birth, or who need such a level of care they are shut away from the world.
we chose to terminate a pg for a much rarer abnormality, and we live with that decision every day
as an opinionated teen, i would have said I would "never" have an abortion, as a young naive 20 something pg with first child, we also said we would not tx should the question arise - we were financially secure and had a good support network. But 2 healthy toddlers later, when faced with a decision to have a (quite late)tx or not, a decision that would have a huge impact on our existing DC and our wider family, and now living away from family support network, we chose to tx
its each to their own. yes some parents go for tx because they want a perfect baby, others feel it is better for their existing children, others think why should I bring this child into the world knowing it will suffer, need immediate heart surgery, and then possibly still die before it is an adult - and as i said, some choose to carry on and lose the baby before term anyway.
all I can say is, if you have not been in the position of having to make that decison, you cannot KNOW what your decision would be.
and having made your decison of what is best for YOU, at that place and time, does not give you the right to judge someone whose decison is not the same as your own.