@tzimmer_history
(Preface: I'm in favor of the No Kings protests and hope they are huge.)

I don't think those who criticize the protests, or those who attend them, have in mind that many attendees *explicitly* believe that occasionally attending a protest is all one needs to do. I think that the criticism is that (a) this is all many of these people *do* in fact do, because (b) they simply don't reflect on the question at all.
I would guess that a huge chunk of people you could ask at the protest, if you asked what else they are doing to fight fascism, most would say attending protests like this and voting. Those are both important (in my opinion), but it reflects a very limited political imagination.