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.
