I might be completely wrong here, but it seems like a misapplication of the idea of non-agression. You see in non-agression/peaceful protest, you would not seek to hurt people, start fights or do terrorism, but instead will target property, processes and structures, so that you actually do create a lot of inconvenience and force your opponents to take measures. In addition by not being the one to initate violence, you also take the higher moral ground and should garner the sympathies of people.

But, somewhere along the way it became just walking around (usually with the permission and cooperation of the authorities) to shout slogans, show off signs and then go home happy that you made yourself heard and did a democracy. In addition this is also a lot safer, meaning you are not risking anything, and most importantly - dont really have to do anything. And of course somehow believe that the people in power will indeed hear you and enact reform, even tho there is absolutely no incentive for them to ever do so. In additioyn to this, the majority of people, especially those in middle and upper class are simply not used to "violence" - even if that is just breaking things, and it also goes against a lot of social programming about following the rules, and how anything remotely aggressive is absolutely horrible and terrifying. A lot of middle class people have a very bland existence, where the most shocking thing they see is some plot twist in a movie (which is why I think, shows like Game of Thrones had such a big success). So seeing all this violence in real life is absolutely terrifying. Like what if they stop breaking windows and start hurting people? Applying force to things is scary. Walking around creates a sense of purpose, sense of community, makes you feel like you did a lot cause you're tired of all the shouting and walking, and you dont feel uncomfortable from doing things against the rules.

You could also make the argument that a peaceful march or a protest is a precursor to non-peaceful one. As in - look at all these people, we come in peace, to ask you, the people in power, to change things, otherwise we will not remain peaceful.