I mean browsing the Wiki articles in English and German Nietzsche himself already mentions several groups in favor of what HE calls slave morality. Judaism, Christianity, Jesuits, the free press, the democratic movement "(is) the political manifestation of slave morality because of its obsession with freedom and equality". And so on.
The thing is they are likely not going to think of it as "slave morality". That is Nietzsches opinion of them. But if you're talking about "freedom (and equality)" you are likely not perceiving that as slavery. It's Nietzsche for whom those ideas are mere self-deception of the slaves who pretend their vices to be virtues, in order to "rebel" against their oppression without bridging over to master morality. Which he apparently thinks is not very rebellious and something to give up.
I'm not an expert on Nietzsche so if someone is more knowledgeable feel free to correct me, but from what I understand Nietzsche characterizes "Master Morality" as the ability to CREATE morality. "Power" in that sense is not primarily domination, but self-actualization. It's the ability to "pick your own goal". He uses the term "vornehm" which is apparently translated with "noble" and while it also has that connotation in German, the literal meaning of "vornehmen" is "to intent (to do something)", "to make a plan". So the "master" is not necessarily the owner of a slave, but someone who is acting, who has agency over themselves and thus his morality is simply divided into "things that further my goal" (vornehm/noble) and "things that don't" (verächtlich/contemptible). He basically distinguishes less between "good and evil" but more between "success and failure". So it's "good" that comes first, and "bad" that is just a consequence of "not being good".
While in terms of the slave morality it's the other way around. As the slave is deprived of the ability to make their own moral, either by a lack of courage or by the oppression of a master, they essentially have two options, either to adopt a master morality without the ability to act upon it and thus be "immoral" or the development of a slave morality that basically consists of rejecting the master morality and to cherish things which reduce the pain of servitude. So the "evil" comes first and "good" is the absence of evil.
Where the master morality creates moral value based on sentiment, the slave morality rejects such values based on resent(i)ment. Master morality is initial action, slave morality is reaction. And where Nietzsche seems to place no limits on the master morality and sees it as only restraint by the master's volition. He apparently thinks that the slave morality goes too far in the sense that the rejection of "the master", to him means the rejection of self-actualization, the rejection of desire, the rejection of agency, the rejection of oneself.
Usefulness to him is not a value in itself, but a tool that serves a purpose. And by upholding this "usefulness" the slave upholds his own slavery. For him it's something like being forced to work the fields, while someone else is feasting and as a result you stop them from feasting and make them work the fields as well. Meaning you haven't actually ended your slavery, you haven't even gotten rid of the master's morality as you're still serving it, you've just gotten rid of any sense of the master's morality as you're still serving it, but they are no longer benefiting from it. So in a sense you've declared your slavery a virtue in itself, which is likely seen as an ultimate act of submission, because the consequence is that you're arguing that "slavery is your choice" and not just the result of oppression.
Now the question is "are these anarchistic ideals of 'no god, no state, no slave, no master'" expressions of slave morality and of self-enslavement, which rejects once and for all rejects one's own agency and makes oneself the cog in a machine of a master or even a masterless machine, subject to the whims of nature? Or are they the genuine self-expression of the those people.
Like what if you are of the genuine impression that the absence of a tyrant and a society of equals serves the purpose of self-actualization MORE than being the tyrant. Like being a tyrant and having other people with a master morality seeking not to accommodate themselves with my rule but to overthrow me and be the tyrant results in a violent free-for-all, where my "power" to self-actualize is mostly guaranteed by my power to dominate others, meaning I'd spend most of my time wasting my power to preserve my power. Which in terms of "using my power to do what I want to do", is actively detrimental to my own goal. It's immoral, not even because I'd be a douche, but because it'd fail to do what I actually desire to do. So I'd violate my own (master) morality. I'd be a powerless slave of the necessity to dominate.
So while Nietzsche probably sees them as the ultimate act of submission and might be right in some instances and wrong in others, usually these movements themselves would see their exact action as an action as a demand for agency. So it's unlikely that they would call it "slave morality" as this contradicts their own impression. The only place where that might work is probably in terms of religion where the mission statement is often surprisingly close to what Nietzsche describes where the submission to a god is the praised and where "slavery as a choice" is quite literally what idk monks/nuns are, but even they would probably not see it as some internalized oppression but as an act of voluntary self-expression. He might disagree, but he's not the moral arbiter of their morality, is he?
I fear I've made quite some assertions on what I think Nietzsche thinks, so again if people know more about it, feel free to correct the parts that need citations or whatnot.
