There’s a big difference between the rabbis march on Washington during the war and today’s matzvav.
Asking, begging for help during the Holocaust on behalf of a humanitarian cause is different than flying a foreign countrys flag and demanding that the United States assist that country, even though the intent of many demonstrators is that the US help Israel defend its citizens, namely acheinu bnei yisroel.
The rabbis march would only anger goyim who are already extremely antisemitic; this rally could play into the dual loyalty stereotype and other tropes which some goyim might be on the fence about.