Tisha B'Av is not as much a commemoration of a terrible historical event, but rather a recognition of its causes and our inability to change our behavior to undermine the causes which led to our exile. Hatred for fellow Jews. Treating Gdliness and religion in a casual and cynical manner. Removing Gd from our lives. They continue to live and permeate our society (as seen from this article). And for that we fast, and mourn. And that is why people such as Mr. Pfeffer feel threatened.
Saudi FM: We hope Iran uses sanction relief for development, not nefarious activities (Reuters)
from the article: Anshel Pfeffer / It is wrong to fast on Tisha B'Av