The issue isn’t which policy to debate. It’s the fact that you think the only form of growth is agreement. You’re asking what idea could make someone change sides, but why do you think sides are the only thing that matter?
Liberals and conservatives both have blind spots. That’s not controversial. The real danger isn’t in disagreement; it’s in identity-based thinking, where changing your mind feels like betrayal instead of maturity.
People aren’t imprisoned by bad policies.
They’re imprisoned by the fear of being disloyal to their tribe. Maybe the better question isn’t “what issue could change someone’s perspective?” Maybe it’s "What would it take for you to admit your side is wrong about something without needing to flip teams or burn everything down?"
Until you can answer that, you’re not defending truth.
I once asked people on another site, if they found out that their position on global warming was proven to be wrong,
would it actually change the policies that they wanted.
Most people were unable to even consider the issue.
My point was that people were emotionally committed to a world vision they had of the future.
That is what they were part of. The issue of global warming was just a path there.