Just to address your point - the mortality rate is only part of the story.
They are finding that if the virus isn't fatal, it IS causing long term lung damage. And they are still investigating the blood clotting issue that seems to accompany younger people contracting the virus, but that has dangerous implications as well. That is in addition to the fact that the lockdown was never meant to STOP the spread, just slow it enough that hospitals wouldn't become overwhelmed. They are still overwhelmed in MANY parts of the country (mine included). Maintaining social distancing and wearing a mask around other people contributes to keeping the flow of new cases and the hospital loads at manageable levels. Opening things back up and then locking down again if hospitals become overwhelmed again is akin to sticking your finger in a dam full of cracks - it's not an "IF" scenario.
What is going to mitigate this in the future is a vaccine and a better handle on treatments that get people healthy again with minimal long term damage (we're not there yet but there's progress every day). In the meantime, maintaining social distancing and doing our part to keep our germs from spreading to others IS slowing the spread enough to keep medical resources from drowning and buying us precious time - which means if people listen and follow guidelines, things CAN reopen slowly sooner than later. If people don't listen, it's literally going to drag things on longer.