Historical Jesus Agnosticism is Not a Slippery Slope

The fact that we can have little, if any, certainty about a first century itinerant preacher who had little impact during his life outside a small group of illiterate peasant followers doesn't mean that we can't have a reasonable degree of certainty about emperors and generals and politicians who were widely enough known during their lives that their activities were chronicled by their contemporaries.  The notion that questioning the existence of a historical Jesus necessitates tossing out all ancient history is nonsense.