I'm not sure I agree with the logical progression you're presenting here. It's true that sometimes people are mistaken regarding warnings, but I don't think the possibility that warnings could be wrong/insufficient is enough to preclude having them at all. Particularly since it hasn't yet been tried. If people went to VVC expecting warnings and came back saying that actually, not a single warning had helped - then I think it might be time to reevaluate whether or not warnings could be useful. But to be blunt, I don't think one person who doesn't normally utilize warnings saying that warnings are clearly useless is a good measuring stick for the potential success/failure of a warnings policy.

Also:

It is okay to have spaces that privilege risk-taking over risk-prevention, so long as everyone involved is aware that's the case.

I think a big part of the current problem is that people expect Vividcon to be all things to all people, which no con or community could possibly be.

I disagree with the generalizations you're making here. Requesting a change in policy so that basic accommodations are made for people with triggers is not trying to force Vividcon "to be all things for all people" - and various suggestions have been made that would enable people who wanted warnings to be able to access them, and people who didn't want them to be able to ignore them. I doubt you're doing it deliberately, but in this post you're setting up a false dichotomy that then justifies not warning for anything. I think it's particularly harmful considering that a warnings system hasn't even been tried yet.