I mean this only to apply to issues that are controversial in the sense that approximately equally sized groups of qualified people exist on either side. In those cases, people should expect that most of their opinions were picked up socially and reinforced by confirmation bias.

Whereas high integrity politicians pick up their opinions on these topics ... how, exactly?

I doubt that politicians have any more time to self-educate themselves on most issues than I do. And I am quite confident that they have less time to self-educate regarding the small fraction of the issues which I consider to be the most important ones.