Bad information and trolls do us all a great disservice. But shouldn't discount all facts because some people hyperventilate or stir the pot. This virus wasn't a biopreparat weapon made in a lab; that doesn't mean it's not a concern. People doing a simple excel best fit function telling you the whole world would be infected by March shouldn't make you think it isn't capable of rapid, localized exponential growth.
We actually do have some pretty good ideas on when it got here and how, and how long it has been here multiplying. You can see it by the genetic branching of the virus.
https://nextstrain.org/ncovPeople absolutely, with certainty, been sick with it without a diagnosis. That's actually part of the problem, not a point against responding. That means it can become widely spread by people with mild symptoms. It isn't the cases in isolation which are the problem.
Its good to avoid the localized hot spots, but since we have localized community spread in multiple cities, and large amounts of domestic travel, it's almost certain that this will spread to every major city in the next few weeks. Doesn't mean panic. Just means clear eyed view of whats coming.