To your 3 paragraphs:

1: Yes - we assume that words mean the same thing to others when we use them, and it's actually quite tricky to know when you've succeeded in communicating meaning.

2: "with special relativity, space/time referentials are relative to an observer, etc." - this is rather sad and makes me think you're trolling. What does this have to do with language? Nothing.

3: Your belief that we can't describe things in certain ways has you preaching, instead of trying to discover what your interlocutor actually means. "which would make of us an epiphenomenon" - so what? It sounds like you're prepared to derail any conversation by insisting everyone remind themselves that these are PEOPLE saying and thinking these things. Or maybe, more reasonably, you think that everyone ought to have a position about why they aren't constantly saying "I think ...", and you'll only derail when they refuse to admit that they're making an aesthetic choice.