and foreclose possible useful alternative conceptions of the world in the everyday.
There's the key, Slimboy. I would argue fundamentalism isn't a 'useful alternative conception of the world', which includes belief in a 6000 year old humanity.
It is important that realist or positivist conceptions of knowledge and language are opposed because they lead to tyranny in extremis
I would say your style of relativism also leads to tyranny in extremis, as nothing is allowed to be established and built upon. Can we take a sort of middle ground here? Can we agree that while language is poor, it is useful, and that while reality is currently ungraspable in its totality, that we can make some useful assumptions about it?