An ugly mess happens. Which is why I think people would be asking themselves those questions before repealing Obamacare / breaking ADA. I think there's a limit to which politicians can pull tricks on people beyond which society's self-preservation instinct kicks in and people vehemently repeal harmful ideas. I doubt you can create a dystopian future with a single vote; it needs to be done very sneakily so that people won't notice until it's too late.
All you need is a big enough crisis to get people to support suspension of the normal checks and balances. That can happen very quickly, in the right circumstances.
Obamacare / ACA didn't set that policy, the Genetic Information Nondiscrimination Act of 2008 was passed almost unanimously by Congress and signed into law by George W Bush. It's a very popular, bipartisan policy.
ACA dated back to 1990, GINA acted as clarification in terms of genetic predisposition to developing a disease in the future (potential problems) and specifically excluded life, disability, or long-term care insurance. Which arguably made the situation worse.
Obamacare prevented insurance companies from treating active genetic disorders as preexisting conditions.