In Influence: Science and Practice, Robert Cialdini makes the compelling case that (non-legally-binding) petitions have a primary effect on the people signing t

In Influence: Science and Practice, Robert Cialdini makes the compelling case that (non-legally-binding) petitions have a primary effect on the people signing the petition, not the explicit targets of the petition. Signing your name to a statement evokes consistency bias effects, which cause you to commit to those statements. So they are still a useful tool for effecting change; just not for the reasons people might assume.