Doing something that helps you and helps your similarly-situated fellow worker seems like something that would qualify you for a union leadership role.

Further: People do all kinds of unpaid work to make their community or shared experiences better without (most of?) us accusing them of advocating for slavery.

Slavery implies force. What I said explicitly required volunteering.

That's like calling volunteering slavery. Am I a slave for working at my hospital in the summer?

Unpaid work isn't slavery, it's volunteering. It's only slavery if (for example) you're locked up in prison and beaten by a guard if you don't do it.