If the lockdowns last too long, we won’t have sufficient herd immunity built up by fall to temper a potentially dangerous second wave. Getting young, healthy people back into the economy is important for this reason.
We are not aiming for herd immunity. Getting to that point quickly enough to make it a viable solution would have a catastrophic impact on society and the healthcare system, even if we're just sending out "healthy" young people to go get sick.
We are waiting for a vaccine, effective antiviral treatments, better hospital readiness, or a sufficient slowdown in cases for testing and contact tracing to serve as a viable option to suppress the disease.
For my part, I'm not really sure we'd be able to do that last thing effectively; all it takes for us to return to uncontrollable spread is for one cluster to go unrecognized for a short period of time. So honestly, if you're not ready to anticipate multiple waves of correlated disease and social mitigation measures, I'd say we're living on a different planet. There is no quick solution until a vaccine because there is no realistic way to make the virus disappear.
