It's "SPLC", Jason. The SPLC lists about 1,000 hate groups in the United States as of 2019. They are categorized by type:
Your reading of their data suggests that each of these groups has, on average, between one and two dozen members, depending on overlap. It also says that the only white supremacists we should count are those that belong to official groups recognized by the SPLC, which for analysis reasons makes divisions among groups that ordinary people don't. It also fails to provide citations. It also doesn't account for the fact that small numbers of people can have extreme negative effects on society, especially when they have lots of power and money. It checks all the boxes.
What you established is that they count a lot of groups out there. They also count
people which is what I'm using.
The three categories of
people lead to less than 10,000
people each in groups of various sizes. Since there are likely people in two or three categories at once, and maybe even in more than one group at a time, we are looking at less than 10,000
people on whole. At worst it could be, if the "less than 10,000" was closer to 9,000 instead of 4,000, and if there is
absolutely no double counting then close to 30,000
people total.
And remember, as a money-making venture masquerading as a non-profit, the SPLC has a vested interest in making the numbers appear as large as possible. If they can't find 10,000 white supremacists, even with loose standards and double counting, then it is very unlikely there are more than 10,000.