I see your point! Absolutely, a self-appointing system wouldn't help to tackle internalised or unintentional racism, nor would it incline those who are writing it unwittingly to risk tagging with it. We'd probably see a small rise in Choose Not To Warn warnings.

I think, for me, the visibility of action is really important here. It isn't just the curation for the individual, but an acknowledgement from the collective (i.e. OTW and by extension those using warning systems put into place) of the existence of racism within fiction, and the necessity to warn fans for it. I'd like for people to see that it's taken seriously; for it to be as visible as Non-Con and Underage warnings are. I also think it would be helpful in bringing about an awareness and culture of recognising what actually is racism in fanfic and fandom. When people see a fic with a warning for racism, but don't register anything themselves, that might create a disconnect where they'll actually think critically about 'well, why was it tagged with that? what is it that my radar is missing?'

That isn't to say I don't also agree with all you've said regarding a blocking tool, and such. I would want both, ideally - and there's no reason why they can't exist in tandem, as they don't even exist in the same sphere of experience. ^_^