Of course they can, but that is dependent on parents who are fully on board with that, and harsh as it may be to say it, the reality is that many (prospective) parents simply aren't. Either because that's not what they want and won't give the necessary commitment (even if only subconsciously), or simply aren't up to the task no matter how hard they try.
Which is the lesser/greater evil - allowing a potential child with Down's to be terminated because the prospective parent's aren't willing (or able) to give the extra attention and care it needs, or allowing an actual child with Down's to suffer because the parents aren't willing (or able) to give the extra attention and care it needs? I don't have the answer to that - I don't think there is a right or wrong answer really, which is why ultimately I think it should be up to the parents (along with advice and guidance from medical professionals).