Opposition to the ACA is driven by conservative voters' sense of grievance more than their understanding of any particular policy. Thus, repealing the ACA will be popular even if it harms these voters. It's not an unreasonable theory.
It's a bullshit theory because the ACA is more popular than ever among both sides of the isle and any bill that's been brought up has had abysmal approval ratings. Some of you guys really have no idea what you're talking about