It literally isn't, changing/reversing a premise and not adressing the point that was made is not a valid way to counter the initial argument in a logical way.

Just like your proposition that any "small" chance justifies investing "everything" disregards the same argument regarding the precautionary principle of potentially devastating technologies. You've also slipped in an additonal "with no real downside" which you cannot predict with certainty anyways, rendering this argument infalsifiable. At least tsimionescu didn't dare making such a sweeping (but baseless) statement.

Some of us believe that continued AI research is by far the biggest threat to human survival, much bigger for example than climate change or nuclear war (which might cause tremendous misery and reduce the population greatly, but seem very unlikely to kill every single person).

I'm guessing that you think that society is getting worse every year or will eventually collapse, and you hope that continued AI research might prevent that outcome.