As someone who works as a Medical Laboratory Scientist and has worked directly with blood samples being sent to the CDC for Coronavirus testing, I dont think its fear mongering, at all. I know we're having to process samples under a biohazard hood as well as taking extra precautions to prevent aerosols from potentially spreading/contaminating. A vaccine wont be available until the end of the year at the earliest and containment of the disease is gonna be reliant on all the world's governments doing what they're supposed to.
Personally, I dont think the issue is with the virus and its lethality. If you're healthy adult, most seem to be able to fight off the virus with no ill effects so far. The problem is that the virus is demonstrating to be easily transmittable and is able to survive outside the body for some time. This puts the young, elderly, and immunocompromised at a high risk.
A decision on cancel public gatherings/cons is decision that obviously wont need to be made for a few months, like you said, but when cancelling Comiket and the Olympics are being talked about when those are months away, its definitely fair to discuss when Otakon will be happening during the same timeframe.