I think swat's referring to freedom of assembly, which is being threatened by a militarized response
Okay so first off, I'm pretty sure that the reason there's being a militarized response is because most if not all of the protests lately have NOT been peaceful. As an example from the ferguson "protests": Lootings, robberies, pyros, people throwing rocks at police officers and literally wishing death upon them. And that's just what I saw looking at brief amounts footage of the so called "protests."
Second, you summed it already: "responding to the sort of demonstrations that erupted after the Eric Garner grand-jury decision"
I never watched any livestreams of the eric garner "protests" but I'm almost certain that they're similar to the ones at ferguson, feel free to correct me here.