The "unless we know everything, we know nothing" is rab putting words in my mouth to exaggerate me in such a way it looks like nonsense
No, that is just to clearly show that your claim is nonsense.
These were your exact words:
Because until we define the nature of the universe, everything else is just an assumption. A best guess.
That sure seems to sound like that unless we know everything, i.e. define the nature of the universe, then we can't know anything as it is just an assumption or best guess.
So which is it?
Do we actually know things, or is it all just assumptions and guesses?
Don't tell people 'dont do any experiments looking for other dimensions or the nature of our universe because we can be quite comfortable with what we know now"
And no one is doing that.
That has nothing to do with ignoring the mountains of evidence and tests which clearly show that Earth is round, not flat.
Well the members on this forum for one. I have postulated all the above theories such as holographic, simulation and extra dimensions only to be met with ridicule and what a stupid thought it is.
Except you weren't just posting that as an idea by itself. Instead you were using it to dismiss all the evidence that shows Earth is round as we know it.
The universe being a hologram doesn't magically mean Earth isn't round. It would just means it is a round hologram.
The universe being a simulation doesn't magically mean Earth isn't round. It would just means it is a round simulation.
The universe having extra dimensions doesn't magically mean Earth is flat. It may be flat in those extra dimensions, but that doesn't stop it being round in the 3 we know.