Can you point to any examples of online petitions doing something other than filling up inboxes of people who don't wanna sign them?
There are examples of cases, where people were able to make an impact by combining their efforts - Nearly every hour, a petition on Change.org achieves victory . One could say that even in those occasions the role of 1 person is critical. There are also examples of normal people creating change on a large scale (Malala Yousafzai - Wikipedia, the free encyclopedia , Mohamed Bouazizi - Wikipedia, the free encyclopedia ) . So I believe that even signing a petition could play a key role and also the role of 1 person can snowball and mobilize many other people.