The point is that majority support is unnecessary for a thing to exist. In fact, it increasingly appears to be an irrelevant metric in general

I think we're talking past each other here and we agree on objectives, just not on methods.

In response to public opinion outcry, Politicians will first make empty promises, then superficial changes which are easily reversible, and only beyond that actual structural changes which are hard to reverse hence are more permanent.

The latter ones is what I meant before with "permanent". What politicians did in response to the George Floyd demonstrations was all the way up to superficial changes, but not structural changes, hence it didn't take long for things to go back to roughly the way they were, and the underlying problem of police violence in the US of which the George Floyd killing was a symptom, is now the same or even worse.

The only peaceful march kind of demonstrations (so, not things like strikes) which I know of were politicians went all the way to structural changes are the kind which lasted months (and at times they weren't actually peaceful), and it's very hard for people to sustain that without organizing.

This demonstration, on the other hand, lasted a single day. I have never heard of any demonstration that lasted a single day and changed anything in a sustained way ever anywhere in the World. I'll be happy if you find me an example to prove me wrong (as that means there's hope).

I think we both agree on the need for sustained pressure and for people not to grow complacent, and as I see it that means that people have to get involved in grassroots efforts and civil society groups to force that change and keep up the pressure until the change is structural and hence deep and near-irreversible. Merely going to a one-day demonstration won't achieve sustained change, but if it acts as a step to joining said grassroots efforts and civil-society groups that keep working well beyond that demonstration then it's a means to an end.

My point is that loudly celebrating a single day peaceful demonstration without the caveat that "it must be a start not and end", risk making many if not most feel "mission accomplished", become complacent and not do anything further, exactly the opposite of your objective of "sustained push for change were people do not grow complacent".

As I see it, if you want the people to keep on pushing there should be a "what next" after the "good job everybody" in the celebrating of this demonstration, but that's not what I see in the countless threads here in Lemmy: all I see is people celebrating it as if "showing Trump he's not liked" was the whole objective of the thing and it was achieved by this demonstration, as if "showing Trump he's not liked" is anywhere close to enough to achieve a structural change of American politics.

If people were indeed getting into the kind of organizations that can deliver the sustained effort both of us think is required, we would be seeing "this is just the start" kind of statements, but I haven't seen any yet and this together with the historical track record of peaceful demonstrations in US leads me to believe this one isn't a beginning of something more, just a one-off.

Isn't this just admission to stereotyping which is inherently illogical?

The US is an oligarchy. Any actual threat to that would be suppressed. Because these protests were not suppressed, what conclusion can be drawn?