Brazilian isn't a race, and Black isn't a nationality. Incredibly, it's even possible to be both. I hope your confusion has been cleared up.
Are you under the impression that race and nationality are equivalent? If you're asking whether the term is considered dehumanizing, that's been answered for you, and if you're asking why, that's been answered as well. In English, racial and ethnic terms are generally used as adjectives, and we don't use adjectives as nouns when referring to groups of people.
It's far more acceptable than "blacks". It also avoids the issue of associating general search terms for groups of people with sexualized contexts as has unfortunately been done to Asian women and others.
Yes, generally referring to groups of people as pluralized adjectives is considered dehumanizing.
Note that Blacks and the Blacks are both considered offensive and should not be used. Black people is the preferred plural form of Black.
https://www.archives.gov/research/catalog/lcdrg/appendix/black-person
[A]im to use Black as an adjective, not a noun. Also, when describing a group, use Black people instead of just “Blacks.”
https://nabjonline.org/news-media-center/styleguide/#styleguidea
This is for the exact same reason you would not refer to a singular Black person as "a black". If you still have trouble perceiving the issue, consider how jarring the term "a gay" would seem in print.
Yes, but you’ve also said that referring to people as “black” is dehumanising
No. Myself, and the commenter who was being responded to, said that referring to Black people as "blacks" is dehumanizing, which it is, and the context being asked for was an alternative term for an NSFW community. Hopefully that clarifies the issue.
Not exactly sure what you're asking, but no, collective nouns aren't generally pluralized in English, nor is the term appropriate outside of a porn context. Are you a native English speaker?
Exactly right, but the context being discussed is porn.
"Pretty sure they"...
Nope, I'll stop you right there. And the context is porn. Note, again, the term being discussed is not Black, which is perfectly kosher, but referring to Black people as "blacks", which is considered dehumanizing.
As for alternatives, the existing PoC-run reddit communities are called Ebony, GoneWildColor, GWBlackGirls, etc. Hopefully that gives you some insight.
Ebony, or GoneWildColor as the existing reddit community was already named.
From left to right: Liloo, Valery Ponce, and Dulce.