Look at what happened in NY and what is happening now in FL and TX and AZ. Health care systems are reaching or surpassing their ability to treat patients. And that is with the help from quarantine and social distancing and shut down measures.

So knowing that baseline, if we didn't implement any safety measures, the burden on the health care system would grow exponentially.

Assume best case is 10% of the US population has had COVID and that has resulted in 125,000 deaths and hospitals being overwhelmed. If we had fewer or no safety measures, maybe the infections double to 20% of the population. But if hospitals were already maxed out, the death rates due to the additional number of people at the same time could easily have been 2-3 times higher. So instead of 125,000 dead we might have 250,000 dead just from the extra people, and then take that 2-3 times higher because of the hospital impact and that could easily be 500,000 dead right now. Very easily. This thing is legit scary even for modern medicine.