What options do countries have? Any vaccine or cure is at least one year away, if not more. There is no miracle cure (Tweets don't count).
Let's say you are a country with SARS-CoV-2.
So, your goals are A. stop the spread, and B. protect the most vulnerable and C. try to keep the number of hospital visits low enough to not collapse the healthcare system, so that people ending up in hospitals have a chance of making it out alive.
Do you 1. lock down the country hard; or 2. keep the country (semi) open, reaching for herd immunity, or 3. do nothing?
If you do #1: prepare to be locked down until a vaccine/cure exists and gets deployed. This is at least 1.5 years. Are you ready for this? Sure, this keeps the death rate low. If you open the lockdown early, people start dying again. Prolonged lockdown hurts the economy, and the healthcare system will also suffer greatly. If the economy collapses, things go to shit really fast, and don't expect help from the hospitals. And, in general, any immunization within the population will proceed slowly if at all.
If you do #2: some people in the risk groups will die because the virus is everywhere. And, for this choice to work, immunization must be a possibility, so that herd immunity can develop in the first place. Over time, the population may resist the virus.
If you do #3: many people in the risk groups die, the healthcare system collapses and you'll be in a really bad place. The population may become resistent, though.
Option #3 is not really good.
Assume you choose #1, i.e. total lockdown. Once you open up the lockdown, you'll be in situation #2. So why not do #2 directly?
If you don't believe that immunization through exposure to the virus can happen, then #1 is the only choice -- hope for a vaccine and be prepared for economic carnage.
But, in all other cases #2 is the saner alternative. I think this is why Sweden is doing what it's doing.