Should a person allow his ideology to set his default positions?

When people adopt a religion, philosophy, or politics as their own, they often don't think through every issue -- or they've not done so yet. Does accepting the various positions of that ideology as a kind of default amount to accepting them on faith? Or does the principle of "giving the benefit of the doubt" apply here? What should a person do when uncertain? Is full understanding of and agreement with every position required for a person to be an adherent or proponent of some ideology?