I don't think the virus is as well understood as you believe, which is why opening back up now may be premature.
Regardless, the riskiest pre-existing conditions appear to be obesity and hypertension. 57-75% of Americans are obese according to the dedicated Wikipedia page. Also bear in mind there is considerable variance among obesity rates per locale. What's the CFR in obese patients?
Edit: if you can't tell me the CFR in obese patients, you shouldn't be rushing to open everything back up. I don't know why people are silently downvoting but there is nothing incorrect or inconsistent about my comment and I'm just making a suggestion based on what little evidence exists.
Point is there will be more than enough cases to overwhelm hospitals if the virus spreads in earnest. In this respect our population is potentially more vulnerable than, say, much of Europe or parts of Asia.
I don't know why my comment is even being downvoted. There is literally nothing factually incorrect or logically inconsistent about it yet every time I post anything regarding COVID19 I get immediate downvotes.
1. A lot of people are gaining weight at a prodigious rate.
2. Newly minted alcoholics are being created before our very eyes.
3. There are already a bunch of seriously bad haircuts.
And this is just among people that I know who have the luxury of sitting around the house working from home. I imagine the real life consequences for the less fortunate are significantly more serious.
1. This doesn't appear to be a falsifiable position with respect to being overly conservative. Any action that results in the hospitals not being overwhelmed will be taken as somehow likely causing the hospitals not to be overwhelmed. It's not clear by this logic how hospital capacities are ever chosen given various uncertainties in the environment.
2. It commits a status quo bias. Only the risks of deviating from shelter in place are considered. On the one hand we have a virus with a CFR of around 0.5% with fairly well understood vulnerabilities to various parts of the population. On the other we have a completely unprecedented shutdown triggering a 2T spending package and causing record unemployment, with an unknown end goal. Is the risk of continuing down this path somehow less than the risks to the hospitals based on our knowledge of disease?