The virus is contagious as hell and it can take up to 14 days for infected individuals to develop symptoms. Low risk individuals who think they have little to worry about are unwitting carriers of the virus, potentially infecting higher risk family members, neighbors, co-workers, etc. Imagine that you were infected a week ago. How many people have you come in contact with over the last 7 days that you've potentially exposed? Now multiply that by a country of 300 million. This isn't a run-of-the-mill flu bug going around an elementary school.
We can point to a 97-98% survival rate and think "see, that's not so bad." The problem is in order to survive, many are going to need treatment from healthcare professionals. If left unchecked, our healthcare system isn't equipped to have 10...20...30% of the population infected in short order. The mortality rate will rise due to insufficient resources to treat COVID-19, and people suffering from a variety of other ailments which are normally manageable (survivable) will not be able to get the treatment they need because hospitals and ERs are completely overwhelmed.
Among those who survive, many are facing long-term damage to their respiratory system and other side effects.
Nobody knows...with 100% certainty...what the next few weeks will bring. But it seems incredibly negligent to assume it will simply blow over if we continue living our lives normally. The closures and restrictions we see now are designed to limit the spread of the infection to a volume that doctors and hospitals can effectively treat. If the number of infected rises too quickly, the mortality rate will be much higher than 2-3%.