I don't know exactly what they are thinking, but my opinion is that the only way to get to the "worst case scenario" is to effectively allow the virus to spread without significant intervention from public health organizations. Like I have posted on several threads, the more dangerous a virus is, the more people will do to avoid it. Worst case scenarios are not going to happen because people don't actually want themselves or their loved ones to die.
By every single reference I have seen, this virus is more contagious (higher R0) than any influenza, so if left completely unchecked, it would infect as many or more than the flu. But it will not go unchecked. Our public health efforts might not be as effective as Singapore's, but they will be better than zero. Even people taking personal precautions like social distancing and hand washing will greatly slow the spread, not to mention the efforts in treatment, cancelling public gatherings, reducing travel, etc.
Re: 342 - Thanks - great points.