I looked it up, in 2019 there were 89 million 20-39 years olds in the U.S. [0], and 7000 ages 18-39 died dies of covid19 [1]. Mathematically that works out to 1 in 12,714, and would be a bit higher were 18-19 years added to the denominator. I didn't mean to exaggerate this number.
You mentioned family in vulnerable groups. Lets grant common sense, that someone who lives with their Grandparent's isn't going to go clubbing? EDIT: People need to use common sense, and they seem to, even in when they are not being forced.
I wish that we could measure the effectiveness of mitigations. This may be your strongest counterpoint. I end up extrapolating worst case numbers sometimes. I'd love to see you come up with a worst case number. I've got the feeling we could agree on a number, but still might disagree on how we react to that number.
Every weekend the beach bars near the Florida city I'm located in are busy. The majority of people are not wearing masks, sometimes almost nobody, sometimes that includes staff. Some places, with DJs and bands, are literally packed shoulder to shoulder as the night wears on. Like it was 2019 again!
I've also been in NY for part of the pandemic, and keep up with my circle there. As far as I know it's like you said, the Florida beach bar scene would not be tolerated. The rules are a bit stricter in NY, better enforced, with less exceptions, with more state backing.
So why are per capita covid19 deaths higher in NY than in Florida? Florida has 1500 deaths per million, and NY has 2500. [2]
EDIT: I was replying to your points, and don't mean to sidetrack us. Perhaps we need to back up? Do you think it is unreasonable for a young person to go clubbing under any circumstances at the moment? IS a definite 1-2+ years of restrictions worth avoiding a small possible (1/1000 at worst?) chance of harm.
[0] https://www.statista.com/statistics/241488/population-of-the...
[1] https://www.statista.com/statistics/1191568/reported-deaths-...