…[a]ssuming that history is merely didactic and meant to teach lessons as opposed to facts, we must also consider the unintended consequences. Presumably, the reason why we would try to fit other events into 9 Av is to give more significance to 9 Av – it demonstrates the auspiciousness of 9 Av throughout Jewish History. However, the very need to add more significance to 9 Av implies that there isn’t enough significance on its own. 9 Av is somehow lacking, and we need to make it more meaningful. Furthermore, the events themselves become more meaningful because they happened on 9 Av – again implying that these events aren’t intrinsically important, but need the added bonus of occurring on 9 Av. And what of the other tragedies that didn’t happen on 9 Av? Are they somehow less important?
This is not to say that we should not connect the tragedies of Jewish History to 9 Av. On the contrary, we are so far removed from the Hurban that we would need some tragedy in our own lives to begin to grasp what it’s like. Those in the European shtetl during the Crusades and Holocaust knew destruction. They experienced and internalized descruction. For them, remembering the Hurban is something real.
Distorting history for a derasha is a gimmick which cheapens both the day and the events.
Rabbi Josh Yuter, “The Historical Meaning of Tish’a B’av (9 Av)”, Yutopia (8 August 2003) [http://www.joshyuter.com/2003/08/08/judaism/jewish-history/the-historical-meaning-of-tisha-bav-9-av/]