yanno, a roman-style legion deployment would be very effective against this sort of "protest" march.
wouldn't even need to use swords, pilae, or plumbatae - cudgels would do. upgrade the scutum and loricum to make them bulletproof, add a gas-mask, and deploy in ranks and files. compact the rioters with the shields and administer the beat-down. 400 troops in good order could devastate and utterly break a "march" of 100,000 idiots in the space of half an hour.