How do you overcome the "what should you try" problem? That seems to be the primary use of ideology, providing the base justification for rallying people behind

How do you overcome the "what should you try" problem? That seems to be the primary use of ideology, providing the base justification for rallying people behind attempting any given course of action or in cases where you know you'll have an effect but it's not really measurable. In practice even deeply ideological people end up being pragmatic changing course in the face of evidence of things not working or having the intended effects. I'm not sure how I would approach issues like, "should we have slavery or indentured servitude," "should women be considered full persons legally or considered extensions of their husband," "should we have state sponsored religion or let people worship as they please" in a way that's pragmatic and doesn't ultimately rely on ideology or appeal to god/natural order.