But if you get a tiny fraction of those people involved in other things that are useful, doesn't that make the whole event useful?
In general, there is a pretty dramatic drop off in activism the more effort is required. Most people who go to a march are never going to do more than that, and I think it's OK to give them that avenue to have some impact, even if it is small. Especially if you use the event as an opportunity to pull some of them into a deeper level of resistance.
Also, media coverage and normalizing open dissent has some cultural value, even if it isn't directly disrupting fascism. Authoritarianism thrives on fear, and millions of people showing they are not afraid makes all resistance easier.