@Just Enough It discriminates against those who might possibly, in the opinion of someone following an agenda, in the future rely on state benefits.
Until recently, Canada would turn back a wealthy and productive applicant if they had a single disabled child: https://crippledscholar.com/2016/04/19/what-canadas-immigration-policies-say-about-the-status-of-disability-in-canada/
(From the law: "A foreign national is inadmissible on health grounds if their health condition might reasonably be expected to cause excessive demand on health or social services." You can find the text here: https://laws-lois.justice.gc.ca/eng/acts/I-2.5/page-9.html?txthl=health#s-38)
...they're not using the futuristic science of Philip K Dick's Minority Report. They're just using plain, old-fashioned racism.
Is old-fashioned eugenics better?
Even if you're OK with it, Canada's policy wasn't limited to provable conditions like Downs and Fragile-X. Many of the denials were for more speculative diagnoses.