The age-stratified IFR is magnitudes different between people under 40 and people above 70. You can still achieve herd immunity without infecting the vulnerable.
We have become better at treating patients with time as well, we now know that putting people on ventilators is a phenomenally bad idea, oxygen, steroids, and blood thinners is the way to go.
Also, the death rate in the US is higher than in Sweden, so how are those lockdowns working out for you?