Dear OP,

I applaud your effort to promote clear thinking on effects of policy. One thing I wanted to mention is that even programs with weak effects may be eventually worthwhile if there is some cancellation of direct effects of the program by some indirect effects. Even if not worthwhile directly, interventions with "effect cancellation" may perhaps be informative for designing future interventions. People in "mediation analysis" worry about these things a lot.

Analyzing mediation is tricky because it needs strong assumptions.