daffy, i don't think it is really fair to say that a ds child is considered as 'less valuable' to those who would teminate.
it is more about the social, psychological and physical aspect of providing for a ds child - or any child for that matter, but children born with such sydromes are more or less 'children' for life and this places a tremendous pressure on the parents when they become older. some can face that life, some feel they can't, although without the choice i suspect many who believe they couldn't would find the resolve.
as i said it is about personal choice, and i am not really one for disparaging people for making personal choices about their life that i feel uncomfortable with, unless it actually affects me personally