IMHO, the value of the protest is to demonstrate a portion of the electorate does not agree with whatever they are protesting. There are a lot of people in a bubble that seem to think the majority always views things exactly the same as they do. Maybe you will always default do doubling down on the status quo, but some people will eventually inquire as to why someone is willing to inconvenience themselves to protest. Once someone starts to be curious about other people's motivations and reasoning, it often does impact their own opinions, for good or bad.
Don't underestimate the importance of the other reason protests are effective: as a politician, it's very, very scary to look out your window and see thousands of people that are mad enough at you to forgoe their day and instead come yell at you about it. It tends to make them a bit more amenable unless they have enough military power to guaranteed squash mass resistance (which is the case for any American politician).
Exactly. Piercing the bubble is the most important purpose of peacefully protesting in a day of internet silos and media monopolies.
Assuming critics are just reflexively resistant is a convenient way to avoid asking whether the criticism has merit. "They'd get it if they were more curious" is unfalsifiable.
Everyone already knows dissent exists. Polls, social media, elections make that clear. The question is whether street protests add anything to that awareness, and whether the way they're conducted generates curiosity or just irritation. For a lot of people it's the latter, and waving that off doesn't make the problem disappear.