this is a straw man argument

No, it's the reality of investing. It carries risk and you cannot accurately nor consistently predict market moves.

2018 was clearly different, and that fact has been borne out by reality.

It's only "clear" because it's in hindsight. You would have been wrong in 2011 and 2015. What made people think in 2015 that a 6 year bull market would continue an additional 2.5 years? If you're going by gut feelings and probability, then you would have pulled out.

I will not so naively jettison my common sense in deference to the irrational bullishness of the folks

Would you have gone back into the market in January? It seems for now the bottom was Dec 24th and we've already regained ~10%.