There's a difference between not knowing everything and inventing rather specific alternatives which you declare are valid because "we don't know everything".
Not knowing means not knowing. Not "well we don't know so maybe it's...".
It's also not "we don't know so maybe no black swans exist".
Knowing and belief are different things too. I don't know for a fact that the tree outside my house is still there when I'm not looking at it, but I believe it will be.
These discussions get muddy quickly precisely because sometimes you're arguing thinking that you know what the other person believes, which is a bit of an arrogant assumption, and then you're off having an argument with a specter of your own making.
Not knowing means not knowing. Not "well we don't know so maybe it's...".