We aren't talking about whether agnosticism and/or nihilism are unreasonable. We're talking about whether they are impossible tout court.
It's an old tactic the one you're taking, which is to carry off your arguing partner into the weeds of oratorical flourishes and pseudorationalist blow-by-blow point-making. One can make any point they like "tout court", that doesn't mean I am required (or indeed that any useful purpose is served) to spend any mental energy formulating a substantive reply.
Your argument seems to be that there are only ever two possible political positions: pro-status-quo or anti-status-quo. Is it really that simple/non-complex?