Doesn't seam to be such a good heuristic, honestly. Why not look first at what seem to work for (a large sample of) other people?
Then you don't have to follow that complicated evolutionary logic style thinking. (I know it's very trendy right not) In the end Nature isn't smart and can't think.
It's about sane defaults. The effort to validate every reasonable hypothesis is extraordinary, and sometimes impossible. We can't afford to live our lives based only on what conclusions science has been able to come to so far. Making some choices based on ancestral norms is perfectly acceptable and better than many alternatives.