SARS mortality rate is 9.6%.
And nobody even blinked.
Yep. Because that pretty much ensures it's never going to be a widespread threat. The milder nature of COVID-19 actually makes it
more dangerous to society. More deadly diseases burn themselves out. They kill off their hosts before the can replicate. COVID-19, on the other hand, doesn't have life-threatening symptoms for most people who become infected. For many, it has no symptoms at all. It's passed along merrily from person to person without drawing much attention. That makes it much, much harder to deal with as an epidemic. It also makes it more likely to mutate - each replication represents an opportunity to mutate, so a virus that spreads far and wide will be much more likely thwart our efforts at maintaining a reliable vaccine.
In addition, diseases that make people seriously ill are actually more taxing on our health care services, on the economy, on society, that disease that simply kill people. That's a rather cold, utilitarian point of view - but it's true. Hundreds of thousands of hospitalizations due to a new virus (keep in mind this is in addition to all the normal illnesses and flus that our health care services have to deal with) will severely stress our hospitals. Even if the death rate per infection is lower than SARS or H1N1, the overall impact of COVID-19 will be much worse. It already is, and shows little sign of diminishing.